Fix cc scrollbar layer issues with initialization, and use element ids throughout.

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 76 matching lines @@
   bool IsRecycleTree() const;
   bool IsSyncTree() const;
   LayerImpl* FindActiveTreeLayerById(int id);
   LayerImpl* FindPendingTreeLayerById(int id);
   bool PinchGestureActive() const;
   BeginFrameArgs CurrentBeginFrameArgs() const;
   base::TimeDelta CurrentBeginFrameInterval() const;
   gfx::Rect DeviceViewport() const;
   const gfx::Rect ViewportRectForTilePriority() const;
   std::unique_ptr<ScrollbarAnimationController>
-  CreateScrollbarAnimationController(ElementId scroll_element_id);
+  CreateScrollbarAnimationController(ElementId scroll_element_id,
+                                     float initial_opacity);
   void DidAnimateScrollOffset();
   bool use_gpu_rasterization() const;
   GpuRasterizationStatus GetGpuRasterizationStatus() const;
   bool create_low_res_tiling() const;
   bool RequiresHighResToDraw() const;
   bool SmoothnessTakesPriority() const;
   VideoFrameControllerClient* GetVideoFrameControllerClient() const;
   MutatorHost* mutator_host() const {
     return layer_tree_host_impl_->mutator_host();
   }
@@ skipping 27 matching lines @@
 
   void MoveChangeTrackingToLayers();
 
   void ForceRecalculateRasterScales();
 
   LayerImplList::const_iterator begin() const;
   LayerImplList::const_iterator end() const;
   LayerImplList::reverse_iterator rbegin();
   LayerImplList::reverse_iterator rend();
 
-  // TODO(crbug.com/702832): This won't be needed if overlay scrollbars have
-  // element ids.
-  void AddToOpacityAnimationsMap(int id, float opacity);
-
   void SetTransformMutated(ElementId element_id,
                            const gfx::Transform& transform);
   void SetOpacityMutated(ElementId element_id, float opacity);
   void SetFilterMutated(ElementId element_id, const FilterOperations& filters);
 
   int source_frame_number() const { return source_frame_number_; }
   void set_source_frame_number(int frame_number) {
     source_frame_number_ = frame_number;
   }
 
@@ skipping 425 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_