Fix for getContextAttributes which wraps bare dictionary into a Dart type.

sdk/lib/web_gl/dart2js/web_gl_dart2js.dart

 /**
  * 3D programming in the browser.
  */
 library dart.dom.web_gl;
 
 import 'dart:collection';
 import 'dart:_collection-dev' hide deprecated;
 import 'dart:html';
 import 'dart:html_common';
 import 'dart:typed_data';
@@ skipping 2392 matching lines @@
   int getAttribLocation(Program program, String name) native;
 
   @DomName('WebGLRenderingContext.getBufferParameter')
   @DocsEditable()
   @Creates('int|Null')
   @Returns('int|Null')
   Object getBufferParameter(int target, int pname) native;
 
   @DomName('WebGLRenderingContext.getContextAttributes')
   @DocsEditable()
-  ContextAttributes getContextAttributes() native;
+  @Creates('ContextAttributes|=Object')
+  ContextAttributes getContextAttributes() {
+    return convertNativeToDart_ContextAttributes(_getContextAttributes_1());
+  }
+  @JSName('getContextAttributes')
+  @DomName('WebGLRenderingContext.getContextAttributes')
+  @DocsEditable()
+  @Creates('ContextAttributes|=Object')
+  _getContextAttributes_1() native;
 
   @DomName('WebGLRenderingContext.getError')
   @DocsEditable()
   int getError() native;
 
   @DomName('WebGLRenderingContext.getExtension')
   @DocsEditable()
   Object getExtension(String name) native;
 
   @DomName('WebGLRenderingContext.getFramebufferAttachmentParameter')
@@ skipping 461 matching lines @@
 
 
 @DocsEditable()
 @DomName('WebGLVertexArrayObjectOES')
 // http://www.khronos.org/registry/webgl/extensions/OES_vertex_array_object/
 @Experimental() // experimental
 class VertexArrayObject extends Interceptor native "WebGLVertexArrayObjectOES" {
   // To suppress missing implicit constructor warnings.
   factory VertexArrayObject._() { throw new UnsupportedError("Not supported"); }
 }