Plumb physical backing size from RWHV to renderer CC.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index 5b763b59f0be31a0e3ca5d85abe2600be4738438..653564e0d482d12b95345643ae51aa8a11274afb 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -269,6 +269,7 @@ class CONTENT_EXPORT RenderWidget
 
   // Resizes the render widget.
   void Resize(const gfx::Size& new_size,
+              const gfx::Size& physical_backing_size,
               const gfx::Rect& resizer_rect,
               bool is_fullscreen,
               ResizeAck resize_ack);
@@ -277,6 +278,7 @@ class CONTENT_EXPORT RenderWidget
   void OnClose();
   void OnCreatingNewAck();
   virtual void OnResize(const gfx::Size& new_size,
+                        const gfx::Size& physical_backing_size,
                         const gfx::Rect& resizer_rect,
                         bool is_fullscreen);
   void OnChangeResizeRect(const gfx::Rect& resizer_rect);
@@ -501,6 +503,9 @@ class CONTENT_EXPORT RenderWidget
 
   PaintAggregator paint_aggregator_;
 
+  // The size of the view's backing surface in non-DPI-adjusted pixels.
+  gfx::Size physical_backing_size_;
+
   // The area that must be reserved for drawing the resize corner.
   gfx::Rect resizer_rect_;