cc: Remove LayerTreeImpl::root_layer usage outside tests

cc/debug/debug_rect_history.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_DEBUG_DEBUG_RECT_HISTORY_H_
 #define CC_DEBUG_DEBUG_RECT_HISTORY_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 51 matching lines @@
 // the appropriate LayerTreeSettings are enabled.
 class DebugRectHistory {
  public:
   static std::unique_ptr<DebugRectHistory> Create();
 
   ~DebugRectHistory();
 
   // Note: Saving debug rects must happen before layers' change tracking is
   // reset.
   void SaveDebugRectsForCurrentFrame(
-      LayerImpl* root_layer,
+      LayerTreeImpl* tree_impl,
       LayerImpl* hud_layer,
       const LayerImplList& render_surface_layer_list,
       const LayerTreeDebugState& debug_state);
 
   const std::vector<DebugRect>& debug_rects() { return debug_rects_; }
 
  private:
   DebugRectHistory();
 
-  void SavePaintRects(LayerImpl* layer);
+  void SavePaintRects(LayerTreeImpl* tree_impl);
   void SavePropertyChangedRects(const LayerImplList& render_surface_layer_list,
                                 LayerImpl* hud_layer);
   void SaveSurfaceDamageRects(
       const LayerImplList& render_surface_layer_list);
   void SaveScreenSpaceRects(
       const LayerImplList& render_surface_layer_list);
   void SaveTouchEventHandlerRects(LayerTreeImpl* layer);
   void SaveTouchEventHandlerRectsCallback(LayerImpl* layer);
-  void SaveWheelEventHandlerRects(LayerImpl* layer);
+  void SaveWheelEventHandlerRects(LayerTreeImpl* tree_impl);
   void SaveScrollEventHandlerRects(LayerTreeImpl* layer);
   void SaveScrollEventHandlerRectsCallback(LayerImpl* layer);
   void SaveNonFastScrollableRects(LayerTreeImpl* layer);
   void SaveNonFastScrollableRectsCallback(LayerImpl* layer);
   void SaveLayerAnimationBoundsRects(
       const LayerImplList& render_surface_layer_list);
 
   std::vector<DebugRect> debug_rects_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugRectHistory);
 };
 
 }  // namespace cc
 
 #endif  // CC_DEBUG_DEBUG_RECT_HISTORY_H_