Remove WebLayerTreeView::deviceViewportSize(), nothing uses it.

public/platform/WebLayerTreeView.h

 /*
  * Copyright (C) 2011 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:
  *
  * 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 45 matching lines @@
     // Sets the root of the tree. The root is set by way of the constructor.
     virtual void setRootLayer(const WebLayer&) { }
     virtual void clearRootLayer() { }
 
     virtual void attachCompositorAnimationTimeline(WebCompositorAnimationTimeline*) { }
     virtual void detachCompositorAnimationTimeline(WebCompositorAnimationTimeline*) { }
 
     // View properties ---------------------------------------------------
 
     virtual void setViewportSize(const WebSize& deviceViewportSize) { }
-    // Gives the viewport size in physical device pixels.
-    virtual WebSize deviceViewportSize() const { return WebSize(); }
 
     virtual void setDeviceScaleFactor(float) { }
     virtual float deviceScaleFactor() const { return 0; }
 
     // Sets the background color for the viewport.
     virtual void setBackgroundColor(WebColor) { }
 
     // Sets the background transparency for the viewport. The default is 'false'.
     virtual void setHasTransparentBackground(bool) { }
 
@@ skipping 91 matching lines @@
     // Toggles continuous painting
     virtual void setContinuousPaintingEnabled(bool) { }
 
     // Toggles scroll bottleneck rects on the HUD layer
     virtual void setShowScrollBottleneckRects(bool) { }
 };
 
 } // namespace blink
 
 #endif // WebLayerTreeView_h