Replace layer id with Element id for tracking scrollbar animation controllers

cc/trees/layer_tree_host.cc

 // 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.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 770 matching lines @@
   if (root_layer_) {
     for (size_t i = 0; i < info->scrolls.size(); ++i) {
       Layer* layer = LayerById(info->scrolls[i].layer_id);
       if (!layer)
         continue;
       layer->SetScrollOffsetFromImplSide(gfx::ScrollOffsetWithDelta(
           layer->scroll_offset(), info->scrolls[i].scroll_delta));
       SetNeedsUpdateLayers();
     }
     for (size_t i = 0; i < info->scrollbars.size(); ++i) {
-      Layer* layer = LayerById(info->scrollbars[i].layer_id);
+      Layer* layer = LayerByElementId(info->scrollbars[i].element_id);
       if (!layer)
         continue;
       layer->SetScrollbarsHiddenFromImplSide(info->scrollbars[i].hidden);
     }
   }
 
   // This needs to happen after scroll deltas have been sent to prevent top
   // controls from clamping the layout viewport both on the compositor and
   // on the main thread.
   ApplyViewportDeltas(info);
@@ skipping 633 matching lines @@
 LayerListReverseIterator<Layer> LayerTreeHost::rend() {
   return LayerListReverseIterator<Layer>(nullptr);
 }
 
 void LayerTreeHost::SetNeedsDisplayOnAllLayers() {
   for (auto* layer : *this)
     layer->SetNeedsDisplay();
 }
 
 }  // namespace cc