Fixed readPixels not working in Dartium.

tools/dom/templates/html/impl/impl_WebGLRenderingContext.darttemplate

 // Copyright (c) 2013, 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.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(NATIVESPEC)class $CLASSNAME$EXTENDS implements CanvasRenderingContext {
 $!MEMBERS
 
+  @DomName('WebGLRenderingContext.readPixels')
+  @DocsEditable()
+  void readPixels(int x, int y, int width, int height, int format, int type,
+          TypedData pixels) {
+$if DART2JS
+      _readPixels(x, y, width, height, format, type, pixels);
+$else
+      var data = js.toArrayBufferView(pixels);
+      _readPixels(x, y, width, height, format, type, data);
+      for (var i = 0; i < data.length; i++) {
+        pixels[i] = data[i];
+      }
+$endif
+  }
+
   /**
    * Sets the currently bound texture to [data].
    *
    * [data] can be either an [ImageElement], a
    * [CanvasElement], a [VideoElement], [TypedData] or an [ImageData] object.
    *
    * This is deprecated in favor of [texImage2D].
    */
   @Deprecated("Use texImage2D")
   void texImage2DUntyped(int targetTexture, int levelOfDetail,
@@ skipping 47 matching lines @@
   }
 
   /**
    * Set the bufferSubData to [data].
    */
   @Deprecated("Use bufferSubData")
   void bufferSubDataTyped(int target, int offset, TypedData data) {
     bufferSubData(target, offset, data);
   }
 }