Move us to HashSet to avoid the overhead of tracking the order

examples/stocks/lib/main.dart

@@ -5,6 +5,7 @@
 library stocks;
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:ui' as ui;
 

examples/stocks/lib/stock_home.dart

@@ -203,7 +203,7 @@ class StockHomeState extends State<StockHome> {
       stocks: stocks.toList(),
       onAction: _buyStock,
       onOpen: (Stock stock, Key arrowKey) {
-        Set<Key> mostValuableKeys = new Set<Key>();
+        Set<Key> mostValuableKeys = new HashSet<Key>();
         mostValuableKeys.add(arrowKey);
         Navigator.pushNamed(context, '/stock/${stock.symbol}', mostValuableKeys: mostValuableKeys);
       },

packages/cassowary/lib/cassowary.dart

@@ -5,6 +5,7 @@
 /// An implementation of the Cassowary constraint solving algorithm in Dart.
 library cassowary;
 
+import 'dart:collection';
 import 'dart:math';
 
 part 'constraint.dart';

packages/cassowary/lib/solver.dart

@@ -146,13 +146,11 @@ class Solver {
 
   Result removeEditVariable(Variable variable) {
     _EditInfo info = _edits[variable];
-    if (info == null) {
+    if (info == null)
       return Result.unknownEditVariable;
-    }
 
-    if (removeConstraint(info.constraint) != Result.success) {
+    if (removeConstraint(info.constraint) != Result.success)
       return Result.internalSolverError;
-    }
 
     _edits.remove(variable);
     return Result.success;
@@ -173,7 +171,7 @@ class Solver {
   }
 
   Set flushUpdates() {
-    Set updates = new Set();
+    Set updates = new HashSet<dynamic>();
 
     for (Variable variable in _vars.keys) {
       _Symbol symbol = _vars[variable];
@@ -183,12 +181,10 @@ class Solver {
 
       if (variable._applyUpdate(updatedValue) && variable._owner != null) {
         dynamic context = variable._owner.context;
-
+        if (context != null)
-        if (context != null) {
           updates.add(context);
       }
     }
-    }
 
     return updates;
   }
@@ -212,10 +208,9 @@ class Solver {
     }
 
     if (needsCleanup) {
-      for (dynamic item in applied.reversed) {
+      for (dynamic item in applied.reversed)
         undoer(item);
     }
-    }
 
     return result;
   }
@@ -223,9 +218,8 @@ class Solver {
   _Symbol _symbolForVariable(Variable variable) {
     _Symbol symbol = _vars[variable];
 
-    if (symbol != null) {
+    if (symbol != null)
       return symbol;
-    }
 
     symbol = new _Symbol(_SymbolType.external, tick++);
     _vars[variable] = symbol;

packages/flutter/lib/src/gestures/recognizer.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:ui' show Point, Offset;
 
 import 'arena.dart';
@@ -43,7 +44,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   GestureArena _gestureArena;
 
   final List<GestureArenaEntry> _entries = <GestureArenaEntry>[];
-  final Set<int> _trackedPointers = new Set<int>();
+  final Set<int> _trackedPointers = new HashSet<int>();
 
   void handleEvent(PointerEvent event);
   void acceptGesture(int pointer) { }

packages/flutter/lib/src/material/ink_well.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
+
 import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -85,7 +87,7 @@ class _InkResponseState<T extends InkResponse> extends State<T> {
         } // else we're probably in deactivate()
       }
     );
-    _splashes ??= new Set<InkSplash>();
+    _splashes ??= new HashSet<InkSplash>();
     _splashes.add(splash);
     _currentSplash = splash;
     updateHighlight(true);

packages/flutter/lib/src/scheduler/scheduler.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:developer';
 import 'dart:ui' as ui;
 
@@ -142,7 +143,7 @@ abstract class Scheduler extends BindingBase {
 
   int _nextFrameCallbackId = 0; // positive
   Map<int, FrameCallback> _transientCallbacks = <int, FrameCallback>{};
-  final Set<int> _removedIds = new Set<int>();
+  final Set<int> _removedIds = new HashSet<int>();
 
   int get transientCallbackCount => _transientCallbacks.length;
 

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

@@ -81,7 +81,7 @@ abstract class GlobalKey<T extends State<StatefulComponent>> extends Key {
   static final Map<GlobalKey, Element> _registry = new Map<GlobalKey, Element>();
   static final Map<GlobalKey, int> _debugDuplicates = new Map<GlobalKey, int>();
   static final Map<GlobalKey, Set<GlobalKeyRemoveListener>> _removeListeners = new Map<GlobalKey, Set<GlobalKeyRemoveListener>>();
-  static final Set<GlobalKey> _removedKeys = new Set<GlobalKey>();
+  static final Set<GlobalKey> _removedKeys = new HashSet<GlobalKey>();
 
   void _register(Element element) {
     assert(() {
@@ -129,7 +129,7 @@ abstract class GlobalKey<T extends State<StatefulComponent>> extends Key {
   static void registerRemoveListener(GlobalKey key, GlobalKeyRemoveListener listener) {
     assert(key != null);
     Set<GlobalKeyRemoveListener> listeners =
-        _removeListeners.putIfAbsent(key, () => new Set<GlobalKeyRemoveListener>());
+        _removeListeners.putIfAbsent(key, () => new HashSet<GlobalKeyRemoveListener>());
     bool added = listeners.add(listener);
     assert(added);
   }
@@ -160,7 +160,7 @@ abstract class GlobalKey<T extends State<StatefulComponent>> extends Key {
     try {
       for (GlobalKey key in _removedKeys) {
         if (!_registry.containsKey(key) && _removeListeners.containsKey(key)) {
-          Set<GlobalKeyRemoveListener> localListeners = new Set<GlobalKeyRemoveListener>.from(_removeListeners[key]);
+          Set<GlobalKeyRemoveListener> localListeners = new HashSet<GlobalKeyRemoveListener>.from(_removeListeners[key]);
           for (GlobalKeyRemoveListener listener in localListeners)
             listener(key);
         }
@@ -524,7 +524,7 @@ enum _ElementLifecycle {
 
 class _InactiveElements {
   bool _locked = false;
-  final Set<Element> _elements = new Set<Element>();
+  final Set<Element> _elements = new HashSet<Element>();
 
   void _unmount(Element element) {
     assert(element._debugLifecycleState == _ElementLifecycle.inactive);
@@ -897,7 +897,7 @@ abstract class Element<T extends Widget> implements BuildContext {
       ancestor = ancestor._parent;
     if (ancestor != null) {
       assert(ancestor is InheritedElement);
-      _dependencies ??= new Set<InheritedElement>();
+      _dependencies ??= new HashSet<InheritedElement>();
       _dependencies.add(ancestor);
       InheritedElement typedAncestor = ancestor;
       typedAncestor._dependants.add(this);
@@ -1378,7 +1378,7 @@ class ParentDataElement extends _ProxyElement<ParentDataWidget> {
 class InheritedElement extends _ProxyElement<InheritedWidget> {
   InheritedElement(InheritedWidget widget) : super(widget);
 
-  Set<Element> _dependants = new Set<Element>();
+  Set<Element> _dependants = new HashSet<Element>();
 
   void debugDeactivated() {
     assert(() {

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

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
+
 import 'package:flutter/animation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
@@ -98,7 +100,7 @@ class Hero extends StatefulComponent {
   final bool alwaysAnimate;
 
   static Map<Object, HeroHandle> of(BuildContext context, Set<Key> mostValuableKeys) {
-    mostValuableKeys ??= new Set<Key>();
+    mostValuableKeys ??= new HashSet<Key>();
     assert(!mostValuableKeys.contains(null));
     // first we collect ALL the heroes, sorted by their tags
     Map<Object, Map<Key, HeroState>> heroes = <Object, Map<Key, HeroState>>{};
@@ -177,7 +179,7 @@ class HeroState extends State<Hero> implements HeroHandle {
     _HeroManifest result = new _HeroManifest(
       key: _key,
       config: config,
-      sourceStates: new Set<HeroState>.from(<HeroState>[this]),
+      sourceStates: new HashSet<HeroState>.from(<HeroState>[this]),
       currentRect: startRect,
       currentTurns: config.turns.toDouble()
     );
@@ -268,7 +270,7 @@ class _HeroQuestState implements HeroHandle {
     _taken = true;
     Set<HeroState> states = sourceStates;
     if (targetState != null)
-      states = states.union(new Set<HeroState>.from(<HeroState>[targetState]));
+      states = states.union(new HashSet<HeroState>.from(<HeroState>[targetState]));
     return new _HeroManifest(
       key: key,
       config: child,
@@ -351,7 +353,7 @@ class HeroParty {
       assert(to == null || to.sourceStates.length == 1);
       assert(to == null || to.currentTurns.floor() == to.currentTurns);
       HeroState targetState = to != null ? to.sourceStates.elementAt(0) : null;
-      Set<HeroState> sourceStates = from != null ? from.sourceStates : new Set<HeroState>();
+      Set<HeroState> sourceStates = from != null ? from.sourceStates : new HashSet<HeroState>();
       sourceStates.remove(targetState);
       RelativeRect sourceRect = from != null ? from.currentRect :
         new RelativeRect.fromRect(to.currentRect.toRect(animationArea).center & Size.zero, animationArea);
@@ -489,7 +491,7 @@ class HeroController extends NavigatorObserver {
   Set<Key> _getMostValuableKeys() {
     assert(_from != null);
     assert(_to != null);
-    Set<Key> result = new Set<Key>();
+    Set<Key> result = new HashSet<Key>();
     if (_from.settings.mostValuableKeys != null)
       result.addAll(_from.settings.mostValuableKeys);
     if (_to.settings.mostValuableKeys != null)

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

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
+
 import 'package:flutter/rendering.dart';
 
 import 'framework.dart';
@@ -97,7 +99,7 @@ class _MixedViewportElement extends RenderObjectElement<MixedViewport> {
   Map<_ChildKey, Element> _childrenByKey = new Map<_ChildKey, Element>();
 
   /// The child offsets that we've been told are invalid.
-  final Set<int> _invalidIndices = new Set<int>();
+  final Set<int> _invalidIndices = new HashSet<int>();
 
   /// Returns false if any of the previously-cached offsets have been marked as
   /// invalid and need to be updated.

packages/flutter/test/widget/routes_test.dart

@@ -2,13 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 import 'package:test/test.dart';
 
 final List<String> results = <String>[];
 
-Set<TestRoute> routes = new Set<TestRoute>();
+Set<TestRoute> routes = new HashSet<TestRoute>();
 
 class TestRoute extends Route<String> {
   TestRoute(this.name);

packages/flutter_tools/lib/src/commands/analyze.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:convert';
 import 'dart:io';
 
@@ -31,7 +32,7 @@ class AnalyzeCommand extends FlutterCommand {
   @override
   Future<int> runInProject() async {
     Stopwatch stopwatch = new Stopwatch()..start();
-    Set<String> pubSpecDirectories = new Set<String>();
+    Set<String> pubSpecDirectories = new HashSet<String>();
     List<String> dartFiles = argResults.rest.toList();
 
     bool foundAnyInCurrentDirectory = false;

packages/flutter_tools/lib/src/test/remote_listener.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:isolate';
@@ -32,7 +33,7 @@ class RemoteListener {
 
   final Suite _suite;
   final WebSocket _socket;
-  final Set<LiveTest> _liveTests = new Set<LiveTest>();
+  final Set<LiveTest> _liveTests = new HashSet<LiveTest>();
 
   static Future start(String server, Metadata metadata, Function getMain()) async {
     WebSocket socket = await WebSocket.connect(server);