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

sdk/lib/web_gl/dartium/web_gl_dartium.dart

 library dart.dom.web_gl;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide deprecated;
 import 'dart:html';
 import 'dart:html_common';
 import 'dart:nativewrappers';
 import 'dart:typed_data';
 // DO NOT EDIT
@@ skipping 474 matching lines @@
 
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // WARNING: Do not edit - generated code.
 
 
 @DocsEditable()
+/**
+ * The properties of a WebGL rendering context.
+ *
+ * If [alpha] is `true`, then the context has an alpha channel.
+ *
+ * If [antialias] is `true`, then antialiasing is performed by the browser, but
+ * only if the browser's implementation of WebGL supports antialiasing.
+ *
+ * If [depth] is `true`, then the context has a depth buffer of at least 16
+ * bits.
+ *
+ * If [premultipliedAlpha] is `true`, then the context's colors are assumed to
+ * be premultiplied. This means that color values are assumed to have  been
+ * multiplied by their alpha values. If [alpha] is `false`, then this flag is
+ * ignored.
+ *
+ * If [preserveDrawingBuffer] is `false`, then all contents of the context are
+ * cleared. If `true`, then all values will remain until changed or cleared.
+ *
+ * If [stencil] is `true`, then the context has a stencil buffer of at least 8
+ * bits.
+ */
 @DomName('WebGLContextAttributes')
 @Unstable()
 class ContextAttributes extends NativeFieldWrapperClass2 {
   // To suppress missing implicit constructor warnings.
   factory ContextAttributes._() { throw new UnsupportedError("Not supported"); }
 
   @DomName('WebGLContextAttributes.alpha')
   @DocsEditable()
   bool get alpha native "WebGLContextAttributes_alpha_Getter";
 
@@ skipping 2555 matching lines @@
 
 @DocsEditable()
 @DomName('WebGLVertexArrayObjectOES')
 // http://www.khronos.org/registry/webgl/extensions/OES_vertex_array_object/
 @Experimental() // experimental
 class VertexArrayObject extends NativeFieldWrapperClass2 {
   // To suppress missing implicit constructor warnings.
   factory VertexArrayObject._() { throw new UnsupportedError("Not supported"); }
 
 }