Cache viewport rect for tile priority in UpdateTiles

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index 57947cc0775523a30bb857e99c199c8d0615a4bf..5a11419ae8eba189bc566c85cfae41c4a5376887 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -119,7 +119,8 @@ class CC_EXPORT PictureLayerImpl
   float MinimumContentsScale() const;
   float MaximumContentsScale() const;
   void ResetRasterScale();
-  gfx::Rect GetViewportForTilePriorityInContentSpace() const;
+  gfx::Rect GetViewportForTilePriorityInContentSpaceForTesting() const;
+  void CacheViewportForTilePriorityInContentSpace();
   PictureLayerImpl* GetRecycledTwinLayer() const;
 
   void SanityCheckTilingState() const;
@@ -173,6 +174,7 @@ class CC_EXPORT PictureLayerImpl
   // from regular draws. Save a copy of the required draw properties of the last
   // frame that has a valid viewport for prioritizing tiles.
   gfx::Rect visible_rect_for_tile_priority_;
+  gfx::Rect viewport_rect_for_tile_priority_in_content_space_;
 
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };