implement the logic to set tile priorities based on current matrix

cc/picture_layer_impl.h

Index: cc/picture_layer_impl.h
diff --git a/cc/picture_layer_impl.h b/cc/picture_layer_impl.h
index 4288042fecd3950478de24f5f915bf6898ce1107..fdfacf64194a50ef39705c05402bc8dc622756b3 100644
--- a/cc/picture_layer_impl.h
+++ b/cc/picture_layer_impl.h
@@ -38,12 +38,18 @@ public:
   // PushPropertiesTo active tree => pending tree
   void SyncFromActiveLayer(const PictureLayerImpl* other);
 
+  void setBounds(const gfx::Size&);
+  void setContentBounds(const gfx::Size&);
+  void setContentsScale(float contentsScaleX, float contentsScaleY);
 protected:
   PictureLayerImpl(int id);
 
   PictureLayerTilingSet tilings_;
   PicturePile pile_;
 
+  gfx::Transform last_screen_space_transform_;
+  double last_update_time_;
+
   friend class PictureLayer;
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };