Cache viewport rect for tile priority in UpdateTiles

cc/trees/layer_tree_impl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 394 matching lines @@
   bool top_controls_shrink_blink_size_;
 
   float top_controls_height_;
 
   // The up-to-date content offset of the top controls, i.e. the amount that the
   // web contents have been shifted down from the top of the device viewport.
   float top_controls_content_offset_;
   float top_controls_delta_;
   float sent_top_controls_delta_;
 
+  // The cached viewport rect for tile priority since the last call of
+  // UpdateDrawProperties.
+  gfx::Rect viewport_rect_for_tile_priority_;
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_