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

sdk/lib/web_gl/dart2js/web_gl_dart2js.dart

Index: sdk/lib/web_gl/dart2js/web_gl_dart2js.dart
diff --git a/sdk/lib/web_gl/dart2js/web_gl_dart2js.dart b/sdk/lib/web_gl/dart2js/web_gl_dart2js.dart
index 14e3fee9ef5f91af754a4499921fe6849c8dd3d8..4416a725e064e276aca8f57a11a325e73302fee6 100644
--- a/sdk/lib/web_gl/dart2js/web_gl_dart2js.dart
+++ b/sdk/lib/web_gl/dart2js/web_gl_dart2js.dart
@@ -480,6 +480,28 @@ class CompressedTextureS3TC extends Interceptor native "WebGLCompressedTextureS3
 
 
 @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 Interceptor native "WebGLContextAttributes" {
@@ -2456,7 +2478,15 @@ class RenderingContext extends CanvasRenderingContext native "WebGLRenderingCont
 
   @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()