Add a cache of LayerImpl's viewport layer type

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 <map>
 #include <set>
 #include <string>
@@ skipping 171 matching lines @@
   const ScrollNode* CurrentlyScrollingNode() const;
   int LastScrolledScrollNodeIndex() const;
   void SetCurrentlyScrollingNode(ScrollNode* node);
   void ClearCurrentlyScrollingNode();
 
   void SetViewportLayersFromIds(int overscroll_elasticity_layer,
                                 int page_scale_layer_id,
                                 int inner_viewport_scroll_layer_id,
                                 int outer_viewport_scroll_layer_id);
   void ClearViewportLayers();
+  // Sets the viewport layer types. This depends on the viewport layers from
+  // SetViewportLayersFromIds and the viewport layer's scroll_clip_layer_ids.
+  void UpdateViewportLayerTypes();
   LayerImpl* OverscrollElasticityLayer() {
     return LayerById(overscroll_elasticity_layer_id_);
   }
   LayerImpl* PageScaleLayer() { return LayerById(page_scale_layer_id_); }
   void ApplySentScrollAndScaleDeltasFromAbortedCommit();
 
   SkColor background_color() const { return background_color_; }
   void set_background_color(SkColor color) { background_color_ = color; }
 
   bool has_transparent_background() const {
@@ skipping 379 matching lines @@
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_