Merge pull request #3010 from krisgiesing/offscreen_layout

Part 2 of independent layout pipelines

examples/layers/widgets/spinning_mixed.dart

@@ -33,6 +33,7 @@ class Rectangle extends StatelessWidget {
 
 double value;
 RenderObjectToWidgetElement<RenderBox> element;
+BuildOwner owner;
 void attachWidgetTreeToRenderTree(RenderProxyBox container) {
   element = new RenderObjectToWidgetAdapter<RenderBox>(
     container: container,
@@ -70,7 +71,7 @@ void attachWidgetTreeToRenderTree(RenderProxyBox container) {
         mainAxisAlignment: MainAxisAlignment.spaceBetween
       )
     )
-  ).attachToRenderTree(element);
+  ).attachToRenderTree(owner, element);
 }
 
 Duration timeBase;

packages/flutter/benchmark/stocks/build_bench.dart

@@ -34,7 +34,7 @@ void main() {
 
   for (int i = 0; i < _kNumberOfIterations || _kRunForever; ++i) {
     appState.setState(_doNothing);
-    binding.buildDirtyElements();
+    binding.buildOwner.buildDirtyElements();
   }
 
   watch.stop();

packages/flutter/lib/src/widgets/binding.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:developer';
 import 'dart:ui' as ui show window;
 import 'dart:ui' show AppLifecycleState, Locale;
 
@@ -26,6 +25,10 @@ class BindingObserver {
 /// This is the glue that binds the framework to the Flutter engine.
 class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Services, Renderer {
 
+  WidgetFlutterBinding() {
+    buildOwner.onBuildScheduled = ensureVisualUpdate;
+  }
+
   /// Creates and initializes the WidgetFlutterBinding. This constructor is
   /// idempotent; calling it a second time will just return the
   /// previously-created instance.
@@ -35,11 +38,15 @@ class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Service
     return _instance;
   }
 
+  final BuildOwner _buildOwner = new BuildOwner();
+  /// The [BuildOwner] in charge of executing the build pipeline for the
+  /// widget tree rooted at this binding.
+  BuildOwner get buildOwner => _buildOwner;
+
   @override
   void initInstances() {
     super.initInstances();
     _instance = this;
-    BuildableElement.scheduleBuildFor = scheduleBuildFor;
     ui.window.onLocaleChanged = handleLocaleChanged;
     ui.window.onPopRoute = handlePopRoute;
     ui.window.onAppLifecycleStateChanged = handleAppLifecycleStateChanged;
@@ -92,60 +99,9 @@ class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Service
 
   @override
   void beginFrame() {
-    buildDirtyElements();
+    buildOwner.buildDirtyElements();
     super.beginFrame();
-    Element.finalizeTree();
-  }
-
-  List<BuildableElement> _dirtyElements = <BuildableElement>[];
-
-  /// Adds an element to the dirty elements list so that it will be rebuilt
-  /// when buildDirtyElements is called.
-  void scheduleBuildFor(BuildableElement element) {
-    assert(!_dirtyElements.contains(element));
-    assert(element.dirty);
-    if (_dirtyElements.isEmpty)
-      ensureVisualUpdate();
-    _dirtyElements.add(element);
-  }
-
-  static int _elementSort(BuildableElement a, BuildableElement b) {
-    if (a.depth < b.depth)
-      return -1;
-    if (b.depth < a.depth)
-      return 1;
-    if (b.dirty && !a.dirty)
-      return -1;
-    if (a.dirty && !b.dirty)
-      return 1;
-    return 0;
-  }
-
-  /// Builds all the elements that were marked as dirty using schedule(), in depth order.
-  /// If elements are marked as dirty while this runs, they must be deeper than the algorithm
-  /// has yet reached.
-  /// This is called by beginFrame().
-  void buildDirtyElements() {
-    if (_dirtyElements.isEmpty)
-      return;
-    Timeline.startSync('Build');
-    BuildableElement.lockState(() {
-      _dirtyElements.sort(_elementSort);
-      int dirtyCount = _dirtyElements.length;
-      int index = 0;
-      while (index < dirtyCount) {
-        _dirtyElements[index].rebuild();
-        index += 1;
-        if (dirtyCount < _dirtyElements.length) {
-          _dirtyElements.sort(_elementSort);
-          dirtyCount = _dirtyElements.length;
-        }
-      }
-      assert(!_dirtyElements.any((BuildableElement element) => element.dirty));
-      _dirtyElements.clear();
-    }, building: true);
-    assert(_dirtyElements.isEmpty);
-    Timeline.finishSync();
+    buildOwner.finalizeTree();
   }
 
   /// The [Element] that is at the root of the hierarchy (and which wraps the
@@ -157,7 +113,7 @@ class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, Service
       container: renderView,
       debugShortDescription: '[root]',
       child: app
-    ).attachToRenderTree(_renderViewElement);
+    ).attachToRenderTree(buildOwner, _renderViewElement);
     beginFrame();
   }
 }
@@ -205,10 +161,11 @@ class RenderObjectToWidgetAdapter<T extends RenderObject> extends RenderObjectWi
   @override
   void updateRenderObject(BuildContext context, RenderObject renderObject) { }
 
-  RenderObjectToWidgetElement<T> attachToRenderTree([RenderObjectToWidgetElement<T> element]) {
-    BuildableElement.lockState(() {
+  RenderObjectToWidgetElement<T> attachToRenderTree(BuildOwner owner, [RenderObjectToWidgetElement<T> element]) {
+    owner.lockState(() {
       if (element == null) {
         element = createElement();
+        element.assignOwner(owner);
         element.mount(null, null);
       } else {
         element.update(this);
@@ -229,7 +186,7 @@ class RenderObjectToWidgetAdapter<T extends RenderObject> extends RenderObjectWi
 /// whose container is the RenderView that connects to the Flutter engine. In
 /// this usage, it is normally instantiated by the bootstrapping logic in the
 /// WidgetFlutterBinding singleton created by runApp().
-class RenderObjectToWidgetElement<T extends RenderObject> extends RenderObjectElement {
+class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObjectElement {
   RenderObjectToWidgetElement(RenderObjectToWidgetAdapter<T> widget) : super(widget);
 
   @override

packages/flutter/lib/src/widgets/framework.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:developer';
 
 import 'debug.dart';
 
@@ -613,17 +614,15 @@ class _InactiveElements {
     });
   }
 
-  void unmountAll() {
-    BuildableElement.lockState(() {
-      try {
-        _locked = true;
-        for (Element element in _elements)
-          _unmount(element);
-      } finally {
-        _elements.clear();
-        _locked = false;
-      }
-    });
+  void _unmountAll() {
+    try {
+      _locked = true;
+      for (Element element in _elements)
+        _unmount(element);
+    } finally {
+      _elements.clear();
+      _locked = false;
+    }
   }
 
   void _deactivateRecursively(Element element) {
@@ -652,8 +651,6 @@ class _InactiveElements {
   }
 }
 
-final _InactiveElements _inactiveElements = new _InactiveElements();
-
 typedef void ElementVisitor(Element element);
 
 abstract class BuildContext {
@@ -667,6 +664,120 @@ abstract class BuildContext {
   void visitChildElements(void visitor(Element element));
 }
 
+class BuildOwner {
+  BuildOwner({ this.onBuildScheduled });
+
+  /// Called on each build pass when the first buildable element is marked dirty
+  VoidCallback onBuildScheduled;
+
+  final _InactiveElements _inactiveElements = new _InactiveElements();
+
+  final List<BuildableElement> _dirtyElements = <BuildableElement>[];
+
+  /// Adds an element to the dirty elements list so that it will be rebuilt
+  /// when buildDirtyElements is called.
+  void scheduleBuildFor(BuildableElement element) {
+    assert(!_dirtyElements.contains(element));
+    assert(element.dirty);
+    if (_dirtyElements.isEmpty && onBuildScheduled != null)
+      onBuildScheduled();
+    _dirtyElements.add(element);
+  }
+
+  int _debugStateLockLevel = 0;
+  bool get _debugStateLocked => _debugStateLockLevel > 0;
+  bool _debugBuilding = false;
+  BuildableElement _debugCurrentBuildTarget;
+
+  /// Establishes a scope in which widget build functions can run.
+  ///
+  /// Inside a build scope, widget build functions are allowed to run, but
+  /// State.setState() is forbidden. This mechanism prevents build functions
+  /// from transitively requiring other build functions to run, potentially
+  /// causing infinite loops.
+  ///
+  /// After unwinding the last build scope on the stack, the framework verifies
+  /// that each global key is used at most once and notifies listeners about
+  /// changes to global keys.
+  void lockState(void callback(), { bool building: false }) {
+    assert(_debugStateLockLevel >= 0);
+    assert(() {
+      if (building) {
+        assert(!_debugBuilding);
+        assert(_debugCurrentBuildTarget == null);
+        _debugBuilding = true;
+      }
+      _debugStateLockLevel += 1;
+      return true;
+    });
+    try {
+      callback();
+    } finally {
+      assert(() {
+        _debugStateLockLevel -= 1;
+        if (building) {
+          assert(_debugBuilding);
+          assert(_debugCurrentBuildTarget == null);
+          _debugBuilding = false;
+        }
+        return true;
+      });
+    }
+    assert(_debugStateLockLevel >= 0);
+  }
+
+  static int _elementSort(BuildableElement a, BuildableElement b) {
+    if (a.depth < b.depth)
+      return -1;
+    if (b.depth < a.depth)
+      return 1;
+    if (b.dirty && !a.dirty)
+      return -1;
+    if (a.dirty && !b.dirty)
+      return 1;
+    return 0;
+  }
+
+  /// Builds all the elements that were marked as dirty using schedule(), in depth order.
+  /// If elements are marked as dirty while this runs, they must be deeper than the algorithm
+  /// has yet reached.
+  /// This is called by beginFrame().
+  void buildDirtyElements() {
+    if (_dirtyElements.isEmpty)
+      return;
+    Timeline.startSync('Build');
+    lockState(() {
+      _dirtyElements.sort(_elementSort);
+      int dirtyCount = _dirtyElements.length;
+      int index = 0;
+      while (index < dirtyCount) {
+        _dirtyElements[index].rebuild();
+        index += 1;
+        if (dirtyCount < _dirtyElements.length) {
+          _dirtyElements.sort(_elementSort);
+          dirtyCount = _dirtyElements.length;
+        }
+      }
+      assert(!_dirtyElements.any((BuildableElement element) => element.dirty));
+      _dirtyElements.clear();
+    }, building: true);
+    assert(_dirtyElements.isEmpty);
+    Timeline.finishSync();
+  }
+
+  /// Complete the element build pass by unmounting any elements that are no
+  /// longer active.
+  /// This is called by beginFrame().
+  void finalizeTree() {
+    lockState(() {
+      _inactiveElements._unmountAll();
+    });
+    assert(GlobalKey._debugCheckForDuplicates);
+    scheduleMicrotask(GlobalKey._notifyListeners);
+  }
+
+}
+
 /// Elements are the instantiations of Widget configurations.
 ///
 /// Elements can, in principle, have children. Only subclasses of
@@ -696,6 +807,10 @@ abstract class Element implements BuildContext {
   Widget get widget => _widget;
   Widget _widget;
 
+  BuildOwner _owner;
+  /// The owner for this node (null if unattached).
+  BuildOwner get owner => _owner;
+
   bool _active = false;
 
   RenderObject get renderObject {
@@ -721,7 +836,7 @@ abstract class Element implements BuildContext {
   @override
   void visitChildElements(void visitor(Element element)) {
     // don't allow visitChildElements() during build, since children aren't necessarily built yet
-    assert(!BuildableElement._debugStateLocked);
+    assert(owner == null || !owner._debugStateLocked);
     visitChildren(visitor);
   }
 
@@ -774,12 +889,6 @@ abstract class Element implements BuildContext {
     return inflateWidget(newWidget, newSlot);
   }
 
-  static void finalizeTree() {
-    _inactiveElements.unmountAll();
-    assert(GlobalKey._debugCheckForDuplicates);
-    scheduleMicrotask(GlobalKey._notifyListeners);
-  }
-
   /// Called when an Element is given a new parent shortly after having been
   /// created. Use this to initialize state that depends on having a parent. For
   /// state that is independent of the position in the tree, it's better to just
@@ -796,6 +905,8 @@ abstract class Element implements BuildContext {
     _slot = newSlot;
     _depth = _parent != null ? _parent.depth + 1 : 1;
     _active = true;
+    if (parent != null) // Only assign ownership if the parent is non-null
+      _owner = parent.owner;
     if (widget.key is GlobalKey) {
       final GlobalKey key = widget.key;
       key._register(this);
@@ -874,7 +985,7 @@ abstract class Element implements BuildContext {
     if (element._parent != null && !element._parent.detachChild(element))
       return null;
     assert(element._parent == null);
-    _inactiveElements.remove(element);
+    owner._inactiveElements.remove(element);
     return element;
   }
 
@@ -914,7 +1025,7 @@ abstract class Element implements BuildContext {
     assert(child._parent == this);
     child._parent = null;
     child.detachRenderObject();
-    _inactiveElements.add(child); // this eventually calls child.deactivate()
+    owner._inactiveElements.add(child); // this eventually calls child.deactivate()
   }
 
   void _activateWithParent(Element parent, dynamic newSlot) {
@@ -1117,8 +1228,6 @@ class ErrorWidget extends LeafRenderObjectWidget {
   RenderBox createRenderObject(BuildContext context) => new RenderErrorBox(message);
 }
 
-typedef void BuildScheduler(BuildableElement element);
-
 /// Base class for instantiations of widgets that have builders and can be
 /// marked dirty.
 abstract class BuildableElement extends Element {
@@ -1139,50 +1248,6 @@ abstract class BuildableElement extends Element {
     return true;
   }
 
-  static BuildScheduler scheduleBuildFor;
-
-  static int _debugStateLockLevel = 0;
-  static bool get _debugStateLocked => _debugStateLockLevel > 0;
-  static bool _debugBuilding = false;
-  static BuildableElement _debugCurrentBuildTarget;
-
-  /// Establishes a scope in which widget build functions can run.
-  ///
-  /// Inside a build scope, widget build functions are allowed to run, but
-  /// State.setState() is forbidden. This mechanism prevents build functions
-  /// from transitively requiring other build functions to run, potentially
-  /// causing infinite loops.
-  ///
-  /// After unwinding the last build scope on the stack, the framework verifies
-  /// that each global key is used at most once and notifies listeners about
-  /// changes to global keys.
-  static void lockState(void callback(), { bool building: false }) {
-    assert(_debugStateLockLevel >= 0);
-    assert(() {
-      if (building) {
-        assert(!_debugBuilding);
-        assert(_debugCurrentBuildTarget == null);
-        _debugBuilding = true;
-      }
-      _debugStateLockLevel += 1;
-      return true;
-    });
-    try {
-      callback();
-    } finally {
-      assert(() {
-        _debugStateLockLevel -= 1;
-        if (building) {
-          assert(_debugBuilding);
-          assert(_debugCurrentBuildTarget == null);
-          _debugBuilding = false;
-        }
-        return true;
-      });
-    }
-    assert(_debugStateLockLevel >= 0);
-  }
-
   /// Marks the element as dirty and adds it to the global list of widgets to
   /// rebuild in the next frame.
   ///
@@ -1194,10 +1259,11 @@ abstract class BuildableElement extends Element {
     assert(_debugLifecycleState != _ElementLifecycle.defunct);
     if (!_active)
       return;
+    assert(owner != null);
     assert(_debugLifecycleState == _ElementLifecycle.active);
     assert(() {
-      if (_debugBuilding) {
-        if (_debugCurrentBuildTarget == null) {
+      if (owner._debugBuilding) {
+        if (owner._debugCurrentBuildTarget == null) {
           // If _debugCurrentBuildTarget is null, we're not actually building a
           // widget but instead building the root of the tree via runApp.
           // TODO(abarth): Remove these cases and ensure that we always have
@@ -1206,7 +1272,7 @@ abstract class BuildableElement extends Element {
         }
         bool foundTarget = false;
         visitAncestorElements((Element element) {
-          if (element == _debugCurrentBuildTarget) {
+          if (element == owner._debugCurrentBuildTarget) {
             foundTarget = true;
             return false;
           }
@@ -1215,7 +1281,7 @@ abstract class BuildableElement extends Element {
         if (foundTarget)
           return true;
       }
-      if (_debugStateLocked && (!_debugAllowIgnoredCallsToMarkNeedsBuild || !dirty)) {
+      if (owner._debugStateLocked && (!_debugAllowIgnoredCallsToMarkNeedsBuild || !dirty)) {
         throw new FlutterError(
           'setState() or markNeedsBuild() called during build.\n'
           'This widget cannot be marked as needing to build because the framework '
@@ -1232,8 +1298,7 @@ abstract class BuildableElement extends Element {
     if (dirty)
       return;
     _dirty = true;
-    assert(scheduleBuildFor != null);
-    scheduleBuildFor(this);
+    owner.scheduleBuildFor(this);
   }
 
   /// Called by the binding when scheduleBuild() has been called to mark this
@@ -1246,17 +1311,17 @@ abstract class BuildableElement extends Element {
       return;
     }
     assert(_debugLifecycleState == _ElementLifecycle.active);
-    assert(_debugStateLocked);
+    assert(owner._debugStateLocked);
     BuildableElement debugPreviousBuildTarget;
     assert(() {
-      debugPreviousBuildTarget = _debugCurrentBuildTarget;
-      _debugCurrentBuildTarget = this;
+      debugPreviousBuildTarget = owner._debugCurrentBuildTarget;
+      owner._debugCurrentBuildTarget = this;
      return true;
     });
     performRebuild();
     assert(() {
-      assert(_debugCurrentBuildTarget == this);
-      _debugCurrentBuildTarget = debugPreviousBuildTarget;
+      assert(owner._debugCurrentBuildTarget == this);
+      owner._debugCurrentBuildTarget = debugPreviousBuildTarget;
       return true;
     });
     assert(!_dirty);
@@ -1879,6 +1944,26 @@ abstract class RenderObjectElement extends BuildableElement {
   }
 }
 
+/// Instantiation of RenderObjectWidgets at the root of the tree
+///
+/// Only root elements may have their owner set explicitly. All other
+/// elements inherit their owner from their parent.
+abstract class RootRenderObjectElement extends RenderObjectElement {
+  RootRenderObjectElement(RenderObjectWidget widget): super(widget);
+
+  void assignOwner(BuildOwner owner) {
+    _owner = owner;
+  }
+
+  @override
+  void mount(Element parent, dynamic newSlot) {
+    // Root elements should never have parents
+    assert(parent == null);
+    assert(newSlot == null);
+    super.mount(parent, newSlot);
+  }
+}
+
 /// Instantiation of RenderObjectWidgets that have no children
 class LeafRenderObjectElement extends RenderObjectElement {
   LeafRenderObjectElement(LeafRenderObjectWidget widget): super(widget);

packages/flutter/lib/src/widgets/mixed_viewport.dart

@@ -252,7 +252,7 @@ class _MixedViewportElement extends RenderObjectElement {
       _resetCache();
       _lastLayoutConstraints = constraints;
     }
-    BuildableElement.lockState(() {
+    owner.lockState(() {
       _doLayout(constraints);
     }, building: true);
   }

packages/flutter/lib/src/widgets/virtual_viewport.dart

@@ -157,7 +157,7 @@ abstract class VirtualViewportElement extends RenderObjectElement {
     assert(startOffsetBase != null);
     assert(startOffsetLimit != null);
     _updatePaintOffset();
-    BuildableElement.lockState(_materializeChildren, building: true);
+    owner.lockState(_materializeChildren, building: true);
   }
 
   void _materializeChildren() {

packages/flutter/test/widget/independent_widget_layout_test.dart

@@ -0,0 +1,163 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:test/test.dart';
+
+const Size _kTestViewSize = const Size(800.0, 600.0);
+
+class OffscreenRenderView extends RenderView {
+  OffscreenRenderView() {
+    configuration = new ViewConfiguration(size: _kTestViewSize);
+  }
+
+  @override
+  void scheduleInitialFrame() {
+    scheduleInitialLayout();
+    scheduleInitialPaint(new TransformLayer(transform: new Matrix4.identity()));
+    // Don't call Scheduler.instance.ensureVisualUpdate()
+  }
+
+  @override
+  void compositeFrame() {
+    // Don't draw to ui.window
+  }
+}
+
+class OffscreenWidgetTree {
+  OffscreenWidgetTree() {
+    renderView.attach(pipelineOwner);
+    renderView.scheduleInitialFrame();
+  }
+
+  final RenderView renderView = new OffscreenRenderView();
+  final BuildOwner buildOwner = new BuildOwner();
+  final PipelineOwner pipelineOwner = new PipelineOwner();
+  RenderObjectToWidgetElement<RenderBox> root;
+
+  void pumpWidget(Widget app) {
+    root = new RenderObjectToWidgetAdapter<RenderBox>(
+      container: renderView,
+      debugShortDescription: '[root]',
+      child: app
+    ).attachToRenderTree(buildOwner, root);
+    pumpFrame();
+  }
+
+  void pumpFrame() {
+    buildOwner.buildDirtyElements();
+    pipelineOwner.flushLayout();
+    pipelineOwner.flushCompositingBits();
+    pipelineOwner.flushPaint();
+    renderView.compositeFrame();
+    if (SemanticsNode.hasListeners) {
+      pipelineOwner.flushSemantics();
+      SemanticsNode.sendSemanticsTree();
+    }
+    buildOwner.finalizeTree();
+  }
+
+}
+
+class Counter {
+  int count = 0;
+}
+
+class Trigger {
+  VoidCallback callback;
+  void fire() {
+    if (callback != null)
+      callback();
+  }
+}
+
+class TriggerableWidget extends StatefulWidget {
+  TriggerableWidget({ this.trigger, this.counter });
+  final Trigger trigger;
+  final Counter counter;
+  @override
+  TriggerableState createState() => new TriggerableState();
+}
+
+class TriggerableState extends State<TriggerableWidget> {
+  @override
+  void initState() {
+    super.initState();
+    config.trigger.callback = this.fire;
+  }
+
+  @override
+  void didUpdateConfig(TriggerableWidget oldConfig) {
+    config.trigger.callback = this.fire;
+  }
+
+  int _count = 0;
+  void fire() {
+    setState(() {
+      _count++;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    config.counter.count++;
+    return new Text("Bang $_count!");
+  }
+}
+
+void main() {
+  test('no crosstalk between widget build owners', () {
+    testWidgets((WidgetTester tester) {
+      Trigger trigger1 = new Trigger();
+      Counter counter1 = new Counter();
+      Trigger trigger2 = new Trigger();
+      Counter counter2 = new Counter();
+      OffscreenWidgetTree tree = new OffscreenWidgetTree();
+      // Both counts should start at zero
+      expect(counter1.count, equals(0));
+      expect(counter2.count, equals(0));
+      // Lay out the "onscreen" in the default test binding
+      tester.pumpWidget(new TriggerableWidget(trigger: trigger1, counter: counter1));
+      // Only the "onscreen" widget should have built
+      expect(counter1.count, equals(1));
+      expect(counter2.count, equals(0));
+      // Lay out the "offscreen" in a separate tree
+      tree.pumpWidget(new TriggerableWidget(trigger: trigger2, counter: counter2));
+      // Now both widgets should have built
+      expect(counter1.count, equals(1));
+      expect(counter2.count, equals(1));
+      // Mark both as needing layout
+      trigger1.fire();
+      trigger2.fire();
+      // Marking as needing layout shouldn't immediately build anything
+      expect(counter1.count, equals(1));
+      expect(counter2.count, equals(1));
+      // Pump the "onscreen" layout
+      tester.pump();
+      // Only the "onscreen" widget should have rebuilt
+      expect(counter1.count, equals(2));
+      expect(counter2.count, equals(1));
+      // Pump the "offscreen" layout
+      tree.pumpFrame();
+      // Now both widgets should have rebuilt
+      expect(counter1.count, equals(2));
+      expect(counter2.count, equals(2));
+      // Mark both as needing layout, again
+      trigger1.fire();
+      trigger2.fire();
+      // Now pump the "offscreen" layout first
+      tree.pumpFrame();
+      // Only the "offscreen" widget should have rebuilt
+      expect(counter1.count, equals(2));
+      expect(counter2.count, equals(3));
+      // Pump the "onscreen" layout
+      tester.pump();
+      // Now both widgets should have rebuilt
+      expect(counter1.count, equals(3));
+      expect(counter2.count, equals(3));
+    });
+  });
+}

packages/flutter_test/lib/src/widget_tester.dart

@@ -38,9 +38,9 @@ class _SteppedWidgetFlutterBinding extends WidgetFlutterBinding {
   // Pump the rendering pipeline up to the given phase.
   @override
   void beginFrame() {
-    buildDirtyElements();
+    buildOwner.buildDirtyElements();
     _beginFrame();
-    Element.finalizeTree();
+    buildOwner.finalizeTree();
   }
 
   // Cloned from Renderer.beginFrame() but with early-exit semantics.
@@ -84,7 +84,7 @@ class WidgetTester extends Instrumentation {
   final FakeAsync async;
   final Clock clock;
 
-  /// Calls [runApp()] with the given widget, then triggers a frame sequent and
+  /// Calls [runApp()] with the given widget, then triggers a frame sequence and
   /// flushes microtasks, by calling [pump()] with the same duration (if any).
   /// The supplied EnginePhase is the final phase reached during the pump pass;
   /// if not supplied, the whole pass is executed.