Implementation of device metrics emulation in render view.

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
===================================================================
--- content/renderer/gpu/render_widget_compositor.h	(revision 221161)
+++ content/renderer/gpu/render_widget_compositor.h	(working copy)
@@ -53,6 +53,8 @@
   int GetLayerTreeId() const;
   void NotifyInputThrottledUntilCommit();
   const cc::Layer* GetRootLayer() const;
+  // Pass zero to cancel overriding.
+  void OverrideDeviceScaleFactor(float device_scale);

[aelias_OOO_until_Jul13, 2013/09/13 23:51:44]

Obsolete?

[dgozman, 2013/09/14 07:42:42]

Nope. This is to ensure that compositor has the real deviceScaleFactor instead
of emulated one passed from blink.

[aelias_OOO_until_Jul13, 2013/09/14 07:53:10]

Hmm, in that case I would prefer that your override be made within Blink at the
moment of passing the device_scale_factor to CC, instead of overriding it on the
side here.

[dgozman, 2013/09/19 10:17:11]

Done.

 
   // WebLayerTreeView implementation.
   virtual void setSurfaceReady();
@@ -120,6 +122,9 @@
   bool threaded_;
   bool suppress_schedule_composite_;
   RenderWidget* widget_;
+  // This stores the original device scale to restore back after device scale
+  // override is canceled. Zero means no override is in place.
+  float saved_device_scale_factor_;
   scoped_ptr<cc::LayerTreeHost> layer_tree_host_;
 };