[DevTools] Use device metrics emulation implemented in content.

Source/core/platform/ScrollView.h

 /*
  * Copyright (C) 2004, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Holger Hans Peter Freyther
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 112 matching lines @@
     virtual IntRect visibleContentRect(VisibleContentRectIncludesScrollbars = ExcludeScrollbars) const OVERRIDE;
     IntSize visibleSize() const { return visibleContentRect().size(); }
     virtual int visibleWidth() const OVERRIDE { return visibleContentRect().width(); }
     virtual int visibleHeight() const OVERRIDE { return visibleContentRect().height(); }
 
     // visibleContentRect().size() is computed from unscaledVisibleContentSize() divided by the value of visibleContentScaleFactor.
     // For the main frame, visibleContentScaleFactor is equal to the page's pageScaleFactor; it's 1 otherwise.
     IntSize unscaledVisibleContentSize(VisibleContentRectIncludesScrollbars = ExcludeScrollbars) const;
     virtual float visibleContentScaleFactor() const { return 1; }
 
+    // Scale used to convert incoming input events. Usually the same as visibleContentScaleFactor(), unless specifically changed.
+    virtual float inputEventsScaleFactor() const { return 1; }
+
     // Functions for getting/setting the size webkit should use to layout the contents. By default this is the same as the visible
     // content size. Explicitly setting a layout size value will cause webkit to layout the contents using this size instead.
     IntSize layoutSize(VisibleContentRectIncludesScrollbars = ExcludeScrollbars) const;
     int layoutWidth(VisibleContentRectIncludesScrollbars scrollbarInclusion = ExcludeScrollbars) const { return layoutSize(scrollbarInclusion).width(); }
     int layoutHeight(VisibleContentRectIncludesScrollbars scrollbarInclusion = ExcludeScrollbars) const { return layoutSize(scrollbarInclusion).height(); }
     IntSize fixedLayoutSize() const;
     void setFixedLayoutSize(const IntSize&);
     bool useFixedLayout() const;
     void setUseFixedLayout(bool enable);
 
@@ skipping 213 matching lines @@
     ASSERT(!widget || widget->isScrollView());
     return static_cast<const ScrollView*>(widget);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toScrollView(const ScrollView*);
 
 } // namespace WebCore
 
 #endif // ScrollView_h