Adds DevTools commands for forced viewport override.

third_party/WebKit/Source/core/frame/VisualViewport.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 281 matching lines @@
         if (ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator())
             coordinator->scrollableAreaScrollLayerDidChange(this);
 
         if (!frameHost().settings().inertVisualViewport()) {
             if (Document* document = mainFrame()->document())
                 document->enqueueScrollEventForNode(document);
         }
 
         enqueueScrollEvent();
 
+        frameHost().chromeClient().mainFrameScrollOffsetChanged();
         mainFrame()->loader().client()->didChangeScrollOffset();
         valuesChanged = true;
     }
 
     if (!valuesChanged)
         return false;
 
     InspectorInstrumentation::didUpdateLayout(mainFrame());
     mainFrame()->loader().saveScrollState();
 
@@ skipping 520 matching lines @@
     } else if (graphicsLayer == m_rootTransformLayer.get()) {
         name =  "Root Transform Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink