Tighter native type annotations for some elements returning Lists

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index d57c8743579b594ad058b2b85f6fa3d5c3fc74ee..6c139bdbced56e181bb1050596bed85cb8c5bdc0 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -10506,6 +10506,8 @@ abstract class Element extends Node implements ParentNode, ChildNode native "Ele
   @SupportedBrowser(SupportedBrowser.SAFARI)
   @Experimental()
   // http://dev.w3.org/csswg/css-regions/#dom-region-getregionflowranges
+  @Creates('JSExtendableArray')
+  @Returns('JSExtendableArray')
   List<Range> getRegionFlowRanges() native;
 
   @JSName('webkitRequestFullScreen')
@@ -16387,6 +16389,8 @@ class MediaStream extends EventTarget native "MediaStream" {
 
   @DomName('MediaStream.getAudioTracks')
   @DocsEditable()
+  @Creates('JSExtendableArray')
+  @Returns('JSExtendableArray')
   List<MediaStreamTrack> getAudioTracks() native;
 
   @DomName('MediaStream.getTrackById')
@@ -16395,6 +16399,8 @@ class MediaStream extends EventTarget native "MediaStream" {
 
   @DomName('MediaStream.getVideoTracks')
   @DocsEditable()
+  @Creates('JSExtendableArray')
+  @Returns('JSExtendableArray')
   List<MediaStreamTrack> getVideoTracks() native;
 
   @DomName('MediaStream.removeTrack')