Replace layer id with Element id for tracking scrollbar animation controllers

cc/trees/layer_tree_host_common.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_common.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 146 matching lines @@
 
 LayerTreeHostCommon::ScrollUpdateInfo::ScrollUpdateInfo()
     : layer_id(Layer::INVALID_ID) {}
 
 bool LayerTreeHostCommon::ScrollUpdateInfo::operator==(
     const LayerTreeHostCommon::ScrollUpdateInfo& other) const {
   return layer_id == other.layer_id && scroll_delta == other.scroll_delta;
 }
 
 LayerTreeHostCommon::ScrollbarsUpdateInfo::ScrollbarsUpdateInfo()
-    : layer_id(Layer::INVALID_ID), hidden(true) {}
+    : element_id(), hidden(true) {}
 
-LayerTreeHostCommon::ScrollbarsUpdateInfo::ScrollbarsUpdateInfo(int layer_id,
+LayerTreeHostCommon::ScrollbarsUpdateInfo::ScrollbarsUpdateInfo(ElementId id,
                                                                 bool hidden)
-    : layer_id(layer_id), hidden(hidden) {}
+    : element_id(id), hidden(hidden) {}
 
 bool LayerTreeHostCommon::ScrollbarsUpdateInfo::operator==(
     const LayerTreeHostCommon::ScrollbarsUpdateInfo& other) const {
-  return layer_id == other.layer_id && hidden == other.hidden;
+  return element_id == other.element_id && hidden == other.hidden;
 }
 
 ScrollAndScaleSet::ScrollAndScaleSet()
     : page_scale_delta(1.f),
       top_controls_delta(0.f),
       has_scrolled_by_wheel(false),
       has_scrolled_by_touch(false) {}
 
 ScrollAndScaleSet::~ScrollAndScaleSet() {}
 
@@ skipping 454 matching lines @@
 
 PropertyTrees* GetPropertyTrees(Layer* layer) {
   return layer->layer_tree_host()->property_trees();
 }
 
 PropertyTrees* GetPropertyTrees(LayerImpl* layer) {
   return layer->layer_tree_impl()->property_trees();
 }
 
 }  // namespace cc