Refactor FindScrollLayerForDeviceViewportPoint to use scroll nodes over layer ids

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 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_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <stddef.h>
 
 #include <bitset>
@@ skipping 656 matching lines @@
 
   void UpdateTileManagerMemoryPolicy(const ManagedMemoryPolicy& policy);
 
   // This function should only be called from PrepareToDraw, as DidDrawAllLayers
   // must be called if this helper function is called.  Returns DRAW_SUCCESS if
   // the frame should be drawn.
   DrawResult CalculateRenderPasses(FrameData* frame);
 
   void ClearCurrentlyScrollingNode();
 
-  LayerImpl* FindScrollLayerForDeviceViewportPoint(
+  ScrollNode* FindScrollNodeForDeviceViewportPoint(
       const gfx::PointF& device_viewport_point,
       InputHandler::ScrollInputType type,
       LayerImpl* layer_hit_by_point,
       bool* scroll_on_main_thread,
       uint32_t* main_thread_scrolling_reason) const;
   float DeviceSpaceDistanceToLayer(const gfx::PointF& device_viewport_point,
                                    LayerImpl* layer_impl);
   void StartScrollbarFadeRecursive(LayerImpl* layer);
   void SetManagedMemoryPolicy(const ManagedMemoryPolicy& policy);
 
@@ skipping 182 matching lines @@
   bool has_scrolled_by_touch_;
 
   bool touchpad_and_wheel_scroll_latching_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_