assertion failed: local packages detected via the specialElement list

[jcollins-g]

Head flutter now fires asserts with head dartdoc. This breaks our travis though doesn't block Flutter.

flutter-docs: parsing lib/temp_doc.dart...
flutter-docs: parsing /tmp/pubcacheTQSBDY/hosted/pub.dartlang.org/intl-0.15.7/lib/intl_browser.dart...
flutter-docs: parsing /tmp/pubcacheTQSBDY/hosted/pub.dartlang.org/matcher-0.12.3+1/lib/mirror_matchers.dart...
flutter-docs: parsing /tmp/pubcacheTQSBDY/hosted/pub.dartlang.org/quiver-2.0.1/lib/io.dart...
flutter-docs: parsing /tmp/pubcacheTQSBDY/hosted/pub.dartlang.org/quiver-2.0.1/lib/mirrors.dart...
flutter-docs: parsing /tmp/pubcacheTQSBDY/hosted/pub.dartlang.org/web_socket_channel-1.0.9/lib/html.dart...
flutter-docs:
flutter-docs: Generation failed: 'package:dartdoc/src/model.dart': Failed assertion: line 5732 pos 12: '!(expectNonLocal &&
flutter-docs: packageGraph.packageMap[packageName].documentedWhere ==
flutter-docs: DocumentLocation.local)': is not true.
flutter-docs: dart:core                               _AssertionError._throwNew
flutter-docs: package:dartdoc/src/model.dart 5732:12  new Package.fromPackageMeta
flutter-docs: package:dartdoc/src/model.dart 5341:15  PackageGraph.findOrCreateLibraryFor
flutter-docs: package:dartdoc/src/model.dart 4607:7   new PackageGraph.<fn>
flutter-docs: dart:collection                         __CompactLinkedHashSet&_HashFieldBase&_HashBase&_OperatorEqualsAndHashCode&SetMixin.forEach
flutter-docs: package:dartdoc/src/model.dart 4606:28  new PackageGraph
flutter-docs: package:dartdoc/src/model.dart 6385:16  PackageBuilder.buildPackageGraph
flutter-docs: ===== asynchronous gap ===========================
flutter-docs: dart:async                              _AsyncAwaitCompleter.completeError
flutter-docs: package:dartdoc/src/model.dart          PackageBuilder.buildPackageGraph
flutter-docs: ===== asynchronous gap ===========================
flutter-docs: dart:async                              _asyncThenWrapperHelper
flutter-docs: package:dartdoc/src/model.dart          PackageBuilder.buildPackageGraph
flutter-docs: package:dartdoc/dartdoc.dart 142:26     Dartdoc.generateDocsBase
flutter-docs:
ProcessException: SubprocessLauncher got non-zero exitCode: 255
  Command: /tmp/flutterUXPONS/bin/cache/dart-sdk/bin/dart dev/tools/dartdoc.dart -c --json
#0      SubprocessLauncher.runStreamed (package:dartdoc/src/io_utils.dart:214:7)
<asynchronous suspension>
#1      _buildFlutterDocs (file:///home/travis/build/dart-lang/dartdoc/tool/grind.dart:684:37)
<asynchronous suspension>
#2      buildFlutterDocs (file:///home/travis/build/dart-lang/dartdoc/tool/grind.dart:595:9)
<asynchronous suspension>
#3      _LocalLibraryMirror._invoke (dart:mirrors/runtime/libmirrors_impl.dart:1104:36)
#4      _LocalObjectMirror.invoke (dart:mirrors/runtime/libmirrors_impl.dart:230:25)
#5      TaskDiscovery.discoverDeclaration.<anon> (package:grinder/src/discover_tasks.dart:79:38)
#6      _rootRun (dart:async/zone.dart:1124:13)
#7      _CustomZone.run (dart:async/zone.dart:1021:19)
#8      _runZoned (dart:async/zone.dart:1516:10)
#9      runZoned (dart:async/zone.dart:1463:12)
#10     ZonedValue.withValue (package:grinder/src/utils.dart:112:12)
#11     GrinderTask.execute (package:grinder/src/grinder_task.dart:64:27)
#12     Grinder._invokeTask (package:grinder/src/grinder.dart:193:27)
#13     Grinder.start.<anon> (package:grinder/src/grinder.dart:168:16)
#14     Future.forEach.<anon> (dart:async/future.dart:486:26)
#15     Future.doWhile.<anon> (dart:async/future.dart:528:26)
#16     _RootZone.runUnaryGuarded (dart:async/zone.dart:1314:10)
#17     _RootZone.bindUnaryCallbackGuarded.<anon> (dart:async/zone.dart:1353:26)
#18     _RootZone.runUnary (dart:async/zone.dart:1379:54)
#19     _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
#20     Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
#21     Future._propagateToListeners (dart:async/future_impl.dart:671:32)
#22     Future._complete (dart:async/future_impl.dart:476:7)
#23     _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
#24     _AsyncAwaitCompleter.complete (dart:async/runtime/libasync_patch.dart:28:18)
#25     _completeOnAsyncReturn (dart:async/runtime/libasync_patch.dart:292:13)
#26     testDartdocFlutterPlugin (file:///home/travis/build/dart-lang/dartdoc/tool/grind.dart)
<asynchronous suspension>
#27     _LocalLibraryMirror._invoke (dart:mirrors/runtime/libmirrors_impl.dart:1104:36)
#28     _LocalObjectMirror.invoke (dart:mirrors/runtime/libmirrors_impl.dart:230:25)
#29     TaskDiscovery.discoverDeclaration.<anon> (package:grinder/src/discover_tasks.dart:79:38)
#30     _rootRun (dart:async/zone.dart:1124:13)
#31     _CustomZone.run (dart:async/zone.dart:1021:19)
#32     _runZoned (dart:async/zone.dart:1516:10)
#33     runZoned (dart:async/zone.dart:1463:12)
#34     ZonedValue.withValue (package:grinder/src/utils.dart:112:12)
#35     GrinderTask.execute (package:grinder/src/grinder_task.dart:64:27)
#36     Grinder._invokeTask (package:grinder/src/grinder.dart:193:27)
#37     Grinder.start.<anon> (package:grinder/src/grinder.dart:168:16)
#38     Future.forEach.<anon> (dart:async/future.dart:486:26)
#39     Future.doWhile.<anon> (dart:async/future.dart:528:26)
#40     _RootZone.runUnaryGuarded (dart:async/zone.dart:1314:10)
#41     _RootZone.bindUnaryCallbackGuarded.<anon> (dart:async/zone.dart:1353:26)
#42     Future.doWhile (dart:async/future.dart:543:18)
#43     Future.forEach (dart:async/future.dart:484:12)
#44     Grinder.start (package:grinder/src/grinder.dart:167:21)
#45     runTasks (package:grinder/src/cli.dart:67:39)
<asynchronous suspension>
#46     grind (package:grinder/grinder.dart:46:12)
#47     main (file:///home/travis/build/dart-lang/dartdoc/tool/grind.dart:16:35)