non-duplicate key assert when duplicate keys

[apwilson]

import 'dart:async';

import 'package:flutter/widgets.dart';

final GlobalKey _kKey = new GlobalKey();
Future main() async {
  runApp(new Block(
      children: new List<Widget>.generate(
          3,
          (_) => new Padding(
              padding: const EdgeInsets.all(8.0),
              child: new Container(
                  key: _kKey,
                  width: 100.0,
                  height: 100.0,
                  decoration: new BoxDecoration(
                      backgroundColor: new Color(0xFFFFFF00)))))));
}

Assert:

10:35:01.044: I/flutter : ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
10:35:01.055: I/flutter : The following assertion was thrown building RawGestureDetector([GlobalKey 273613476]; state:
10:35:01.058: I/flutter : RawGestureDetectorState(304216675; gestures: vertical drag; behavior: opaque)):
10:35:01.062: I/flutter : scheduleBuildFor() called for a widget for which a build was already scheduled.
10:35:01.065: I/flutter : The method was called for the following element:
10:35:01.068: I/flutter :   DecoratedBox(dirty; renderObject: RenderDecoratedBox NEEDS-LAYOUT DETACHED)
10:35:01.072: I/flutter : The current dirty list consists of:
10:35:01.075: I/flutter :   [DecoratedBox(dirty; renderObject: RenderDecoratedBox NEEDS-LAYOUT DETACHED)]
10:35:01.078: I/flutter : This usually indicates that a widget was rebuilt outside the build phase (thus marking the element
10:35:01.082: I/flutter : as clean even though it is still in the dirty list). This should not be possible and is probably
10:35:01.085: I/flutter : caused by a bug in the widgets framework. Please report it:
10:35:01.087: I/flutter : https://github.com/flutter/flutter/issues/new
10:35:01.090: I/flutter : To debug this issue, consider setting the debugPrintScheduleBuildForStacks and
10:35:01.093: I/flutter : debugPrintBuildDirtyElements flags to true and looking for a call to scheduleBuildFor for a widget
10:35:01.096: I/flutter : that is labeled "ALREADY IN LIST".
10:35:01.243: I/flutter :
10:35:01.247: I/flutter : When the exception was thrown, this was the stack:
10:35:01.272: I/flutter : #0      BuildOwner.scheduleBuildFor.<anonymous closure> (package:flutter/src/widgets/framework.dart:1531:9)
10:35:01.275: I/flutter : #2      BuildOwner.scheduleBuildFor (package:flutter/src/widgets/framework.dart:1527:12)
10:35:01.278: I/flutter : #3      BuildableElement.markNeedsBuild (package:flutter/src/widgets/framework.dart:2538:11)
10:35:01.282: I/flutter : #4      BuildableElement.dependenciesChanged (package:flutter/src/widgets/framework.dart:2584:5)
10:35:01.285: I/flutter : #5      BuildableElement.activate (package:flutter/src/widgets/framework.dart:2599:7)
10:35:01.289: I/flutter : #6      Element._activateRecursively (package:flutter/src/widgets/framework.dart:2194:13)
10:35:01.292: I/flutter : #7      SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:3424:14)
10:35:01.295: I/flutter : #8      Element._activateRecursively (package:flutter/src/widgets/framework.dart:2196:13)
10:35:01.298: I/flutter : #9      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:2690:14)
10:35:01.301: I/flutter : #10     Element._activateRecursively (package:flutter/src/widgets/framework.dart:2196:13)
10:35:01.305: I/flutter : #11     Element._activateWithParent (package:flutter/src/widgets/framework.dart:2187:5)
10:35:01.307: I/flutter : #12     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2131:18)
10:35:01.310: I/flutter : #13     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.313: I/flutter : #14     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3436:14)
10:35:01.316: I/flutter : #15     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.319: I/flutter : #16     MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3532:32)
10:35:01.322: I/flutter : #17     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.325: I/flutter : #18     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.327: I/flutter : #19     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3436:14)
10:35:01.330: I/flutter : #20     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.333: I/flutter : #21     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.336: I/flutter : #22     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3436:14)
10:35:01.339: I/flutter : #23     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.342: I/flutter : #24     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.346: I/flutter : #25     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3436:14)
10:35:01.349: I/flutter : #26     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.352: I/flutter : #27     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.355: I/flutter : #28     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:3436:14)
10:35:01.358: I/flutter : #29     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.361: I/flutter : #30     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.364: I/flutter : #31     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:2678:16)
10:35:01.367: I/flutter : #32     BuildableElement.rebuild (package:flutter/src/widgets/framework.dart:2567:5)
10:35:01.370: I/flutter : #33     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:2652:5)
10:35:01.373: I/flutter : #34     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:2768:22)
10:35:01.376: I/flutter : #35     ComponentElement.mount (package:flutter/src/widgets/framework.dart:2647:5)
10:35:01.379: I/flutter : #36     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.383: I/flutter : #37     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.386: I/flutter : #38     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:2678:16)
10:35:01.389: I/flutter : #39     BuildableElement.rebuild (package:flutter/src/widgets/framework.dart:2567:5)
10:35:01.392: I/flutter : #40     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:2652:5)
10:35:01.395: I/flutter : #41     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:2768:22)
10:35:01.399: I/flutter : #42     ComponentElement.mount (package:flutter/src/widgets/framework.dart:2647:5)
10:35:01.402: I/flutter : #43     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.405: I/flutter : #44     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.409: I/flutter : #45     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:2678:16)
10:35:01.412: I/flutter : #46     BuildableElement.rebuild (package:flutter/src/widgets/framework.dart:2567:5)
10:35:01.415: I/flutter : #47     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:2652:5)
10:35:01.418: I/flutter : #48     ComponentElement.mount (package:flutter/src/widgets/framework.dart:2647:5)
10:35:01.421: I/flutter : #49     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.424: I/flutter : #50     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.428: I/flutter : #51     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:2678:16)
10:35:01.431: I/flutter : #52     BuildableElement.rebuild (package:flutter/src/widgets/framework.dart:2567:5)
10:35:01.434: I/flutter : #53     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:2652:5)
10:35:01.437: I/flutter : #54     ComponentElement.mount (package:flutter/src/widgets/framework.dart:2647:5)
10:35:01.440: I/flutter : #55     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2139:14)
10:35:01.444: I/flutter : #56     Element.updateChild (package:flutter/src/widgets/framework.dart:1970:12)
10:35:01.447: I/flutter : #57     RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:518:16)
10:35:01.449: I/flutter : #58     RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:489:5)
10:35:01.453: I/flutter : #59     RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:435:17)
10:35:01.456: I/flutter : #60     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:1649:19)
10:35:01.459: I/flutter : #61     RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:434:13)
10:35:01.462: I/flutter : #62     BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding&WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:336:7)
10:35:01.465: I/flutter : #63     runApp (package:flutter/src/widgets/binding.dart:367:7)
10:35:01.468: I/flutter : #64     main.<main_async_body> (/data/user/0/com.google.fuchsia.armadillo/cache/armadillowvraes/lib/main.dart:11:3)
10:35:01.471: I/flutter : (elided 4 frames from class _AssertionError and package dart:async)
10:35:01.475: I/flutter : ════════════════════════════════════════════════════════════════════════════════════════════════════