cc: Remove LayerTreeImpl::root_layer usage outside tests

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 429 matching lines @@
   // Returns the tree LTH synchronizes with.
   LayerTreeImpl* sync_tree() {
     // TODO(enne): This is bogus.  It should return based on the value of
     // CommitToActiveTree() and not whether the pending tree exists.
     return pending_tree_ ? pending_tree_.get() : active_tree_.get();
   }
   virtual void CreatePendingTree();
   virtual void ActivateSyncTree();
 
   // Shortcuts to layers on the active tree.
-  LayerImpl* RootLayer() const;
   LayerImpl* InnerViewportScrollLayer() const;
   LayerImpl* OuterViewportScrollLayer() const;
   LayerImpl* CurrentlyScrollingLayer() const;
 
   int scroll_layer_id_when_mouse_over_scrollbar() const {
     return scroll_layer_id_when_mouse_over_scrollbar_;
   }
   bool scroll_affects_scroll_handler() const {
     return scroll_affects_scroll_handler_;
   }
@@ skipping 230 matching lines @@
       ScrollState* scroll_state,
       LayerImpl* scrolling_layer_impl,
       InputHandler::ScrollInputType type);
   void DistributeScrollDelta(ScrollState* scroll_state);
 
   bool AnimatePageScale(base::TimeTicks monotonic_time);
   bool AnimateScrollbars(base::TimeTicks monotonic_time);
   bool AnimateTopControls(base::TimeTicks monotonic_time);
 
   void TrackDamageForAllSurfaces(
-      LayerImpl* root_draw_layer,
       const LayerImplList& render_surface_layer_list);
 
   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 ClearCurrentlyScrollingLayer();
@@ skipping 156 matching lines @@
       fixed_raster_scale_attempted_scale_change_history_;
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_