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

sdk/lib/html/html_common/conversions.dart

 // 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.
 
 
 // Conversions for IDBKey.
 //
 // Per http://www.w3.org/TR/IndexedDB/#key-construct
 //
 // "A value is said to be a valid key if it is one of the following types: Array
@@ skipping 276 matching lines @@
 
     // Assume anything else is already a valid Dart object, either by having
     // already been processed, or e.g. a clonable native class.
     return e;
   }
 
   var copy = walk(object);
   return copy;
 }
 
+// Conversions for ContextAttributes.
+//
+// On Firefox, the returned ContextAttributes is a plain object.
+class _TypedContextAttributes implements gl.ContextAttributes {
+  bool alpha;
+  bool antialias;
+  bool depth;
+  bool premultipliedAlpha;
+  bool preserveDrawingBuffer;
+  bool stencil;
+
+  _TypedContextAttributes(this.alpha, this.antialias, this.depth,
+      this.premultipliedAlpha, this.preserveDrawingBuffer, this.stencil);
+}
+
+gl.ContextAttributes convertNativeToDart_ContextAttributes(
+    nativeContextAttributes) {
+  if (nativeContextAttributes is gl.ContextAttributes) {
+    return nativeContextAttributes;
+  }
+
+  // On Firefox the above test fails because ContextAttributes is a plain
+  // object so we create a _TypedContextAttributes.
+
+  return new _TypedContextAttributes(
+      JS('var', '#.alpha', nativeContextAttributes),
+      JS('var', '#.antialias', nativeContextAttributes),
+      JS('var', '#.depth', nativeContextAttributes),
+      JS('var', '#.premultipliedAlpha', nativeContextAttributes),
+      JS('var', '#.preserveDrawingBuffer', nativeContextAttributes),
+      JS('var', '#.stencil', nativeContextAttributes));
+}
+
 // Conversions for ImageData
 //
 // On Firefox, the returned ImageData is a plain object.
 
 class _TypedImageData implements ImageData {
   final Uint8ClampedList data;
   final int height;
   final int width;
 
   _TypedImageData(this.data, this.height, this.width);
@@ skipping 44 matching lines @@
 const String _serializedScriptValue =
     'num|String|bool|'
     'JSExtendableArray|=Object|'
     'Blob|File|ByteBuffer|TypedData'
     // TODO(sra): Add Date, RegExp.
     ;
 const annotation_Creates_SerializedScriptValue =
     const Creates(_serializedScriptValue);
 const annotation_Returns_SerializedScriptValue =
     const Returns(_serializedScriptValue);