Updates AutomatedTestWidgetsFlutterBinding.pump to support microsecond precision (#132401)

* Updated `AutomatedTestWidgetsFlutterBinding.pump` to use microseconds instead of milliseconds
* Added a test to prevent regression of the microsecond precision
* Fixed a test that incorrectly assumed millisecond precision

Closes #112610

packages/flutter_test/lib/src/binding.dart

@@ -1257,7 +1257,7 @@ class AutomatedTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
       if (hasScheduledFrame) {
         _currentFakeAsync!.flushMicrotasks();
         handleBeginFrame(Duration(
-          milliseconds: _clock!.now().millisecondsSinceEpoch,
+          microseconds: _clock!.now().microsecondsSinceEpoch,
         ));
         _currentFakeAsync!.flushMicrotasks();
         handleDrawFrame();

packages/flutter_test/test/bindings_test.dart

@@ -12,8 +12,8 @@ library;
 import 'dart:async';
 import 'dart:io';
 
+import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
@@ -57,6 +57,18 @@ void main() {
     order += 1;
   });
 
+  testWidgets('timeStamp should be accurate to microsecond precision', (WidgetTester tester) async {
+    final WidgetsBinding widgetsBinding = WidgetsFlutterBinding.ensureInitialized();
+
+    await tester.pumpWidget(const CircularProgressIndicator());
+
+    final Duration timeStampBefore = widgetsBinding.currentSystemFrameTimeStamp;
+    await tester.pump(const Duration(microseconds: 12345));
+    final Duration timeStampAfter = widgetsBinding.currentSystemFrameTimeStamp;
+
+    expect(timeStampAfter - timeStampBefore, const Duration(microseconds: 12345));
+  });
+
   group('elapseBlocking', () {
     testWidgets('timer is not called', (WidgetTester tester) async {
       bool timerCalled = false;

packages/flutter_test/test/widget_tester_test.dart

@@ -119,12 +119,17 @@ void main() {
 
       await tester.pumpFrames(target, const Duration(milliseconds: 55));
 
-      expect(logPaints, <int>[0, 17000, 34000, 50000]);
+      // `pumpframes` defaults to 16 milliseconds and 683 microseconds per pump,
+      // so we expect 4 pumps of 16683 microseconds each in the 55ms duration.
+      expect(logPaints, <int>[0, 16683, 33366, 50049]);
       logPaints.clear();
 
       await tester.pumpFrames(target, const Duration(milliseconds: 30), const Duration(milliseconds: 10));
 
-      expect(logPaints, <int>[60000, 70000, 80000]);
+      // Since `pumpFrames` was given a 10ms interval per pump, we expect the
+      // results to continue from 50049 with 10000 microseconds per pump over
+      // the 30ms duration.
+      expect(logPaints, <int>[60049, 70049, 80049]);
     });
   });
   group('pageBack', () {