Fixed readPixels not working in Dartium.

tools/dom/templates/html/impl/impl_WebGL2RenderingContext.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 $LIBRARYNAME;
+
+@DocsEditable()
+$(ANNOTATIONS)$(NATIVESPEC)class $CLASSNAME$EXTENDS implements _WebGL2RenderingContextBase, _WebGLRenderingContextBase {
+$!MEMBERS
+
+  @DomName('WebGLRenderingContext2.readPixels')
+  @DocsEditable()
+  void readPixels(int x, int y, int width, int height, int format, int type,
+          TypedData pixels) {
+$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
+  }
+}
+