Make delegated software renderer work on Mac

cc/output/software_output_device.h

Index: cc/output/software_output_device.h
diff --git a/cc/output/software_output_device.h b/cc/output/software_output_device.h
index e371654be4e9d35aeac6661c74e667bad9bea32e..e8de5b905702b8f1b8d139e824f4e72e0717524d 100644
--- a/cc/output/software_output_device.h
+++ b/cc/output/software_output_device.h
@@ -36,7 +36,7 @@ class CC_EXPORT SoftwareOutputDevice {
   // Discards any pre-existing backing buffers and allocates memory for a
   // software device of |size|. This must be called before the
   // |SoftwareOutputDevice| can be used in other ways.
-  virtual void Resize(const gfx::Size& size);
+  virtual void Resize(const gfx::Size& pixel_size, float scale_factor);
 
   // Called on BeginDrawingFrame. The compositor will draw into the returned
   // SkCanvas. The |SoftwareOutputDevice| implementation needs to provide a
@@ -74,7 +74,8 @@ class CC_EXPORT SoftwareOutputDevice {
   virtual gfx::VSyncProvider* GetVSyncProvider();
 
  protected:
-  gfx::Size viewport_size_;
+  gfx::Size viewport_pixel_size_;
+  float scale_factor_;
   gfx::Rect damage_rect_;
   skia::RefPtr<SkCanvas> canvas_;
   scoped_ptr<gfx::VSyncProvider> vsync_provider_;