cc: Use reverse spiral iterator in tiling eviction.

cc/layers/picture_layer_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_LAYERS_PICTURE_LAYER_IMPL_H_
 #define CC_LAYERS_PICTURE_LAYER_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 52 matching lines @@
     size_t current_stage_;
 
     // One low res stage, and three high res stages.
     IterationStage stages_[4];
     PictureLayerTiling::TilingRasterTileIterator iterators_[NUM_ITERATORS];
   };
 
   class CC_EXPORT LayerEvictionTileIterator {
    public:
     LayerEvictionTileIterator();
-    LayerEvictionTileIterator(PictureLayerImpl* layer,
-                              TreePriority tree_priority);
+    explicit LayerEvictionTileIterator(PictureLayerImpl* layer);
     ~LayerEvictionTileIterator();
 
     Tile* operator*();
     const Tile* operator*() const;
     LayerEvictionTileIterator& operator++();
     operator bool() const;
 
    private:
     bool AdvanceToNextCategory();
     bool AdvanceToNextTilingRangeType();
     bool AdvanceToNextTiling();
 
     PictureLayerTilingSet::TilingRange CurrentTilingRange() const;
     size_t CurrentTilingIndex() const;
 
     PictureLayerImpl* layer_;
-    TreePriority tree_priority_;
 
     PictureLayerTiling::EvictionCategory current_category_;
     PictureLayerTilingSet::TilingRangeType current_tiling_range_type_;
     size_t current_tiling_;
     PictureLayerTiling::TilingEvictionTileIterator current_iterator_;
   };
 
   static scoped_ptr<PictureLayerImpl> Create(LayerTreeImpl* tree_impl, int id) {
     return make_scoped_ptr(new PictureLayerImpl(tree_impl, id));
   }
@@ skipping 120 matching lines @@
   // frame that has a valid viewport for prioritizing tiles.
   gfx::Rect visible_rect_for_tile_priority_;
 
   friend class PictureLayer;
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_PICTURE_LAYER_IMPL_H_