Refactor LayerTreeImpl's scrollbar map to be keyed on element ids

cc/input/single_scrollbar_animation_controller_thinning.cc

 // Copyright 2013 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/input/single_scrollbar_animation_controller_thinning.h"
 
 #include <algorithm>
 
 #include "base/memory/ptr_util.h"
 #include "base/time/time.h"
 #include "cc/input/scrollbar_animation_controller.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_impl_base.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
 
 std::unique_ptr<SingleScrollbarAnimationControllerThinning>
 SingleScrollbarAnimationControllerThinning::Create(
-    int scroll_layer_id,
+    ElementId scroll_element_id,
     ScrollbarOrientation orientation,
     ScrollbarAnimationControllerClient* client,
     base::TimeDelta thinning_duration) {
   return base::WrapUnique(new SingleScrollbarAnimationControllerThinning(
-      scroll_layer_id, orientation, client, thinning_duration));
+      scroll_element_id, orientation, client, thinning_duration));
 }
 
 SingleScrollbarAnimationControllerThinning::
     SingleScrollbarAnimationControllerThinning(
-        int scroll_layer_id,
+        ElementId scroll_element_id,
         ScrollbarOrientation orientation,
         ScrollbarAnimationControllerClient* client,
         base::TimeDelta thinning_duration)
     : client_(client),
       is_animating_(false),
-      scroll_layer_id_(scroll_layer_id),
+      scroll_element_id_(scroll_element_id),
       orientation_(orientation),
       captured_(false),
       mouse_is_over_scrollbar_(false),
       mouse_is_near_scrollbar_(false),
       thickness_change_(NONE),
       thinning_duration_(thinning_duration) {
   ApplyThumbThicknessScale(kIdleThicknessScale);
 }
 
 bool SingleScrollbarAnimationControllerThinning::Animate(base::TimeTicks now) {
@@ skipping 125 matching lines @@
 }
 
 void SingleScrollbarAnimationControllerThinning::UpdateThumbThicknessScale() {
   StopAnimation();
   ApplyThumbThicknessScale(mouse_is_near_scrollbar_ ? 1.f
                                                     : kIdleThicknessScale);
 }
 
 void SingleScrollbarAnimationControllerThinning::ApplyThumbThicknessScale(
     float thumb_thickness_scale) {
-  for (ScrollbarLayerImplBase* scrollbar :
-       client_->ScrollbarsFor(scroll_layer_id_)) {
+  for (auto* scrollbar : client_->ScrollbarsFor(scroll_element_id_)) {
     if (scrollbar->orientation() != orientation_)
       continue;
     if (!scrollbar->is_overlay_scrollbar())
       continue;
 
     float scale = AdjustScale(thumb_thickness_scale,
                               scrollbar->thumb_thickness_scale_factor(),
                               thickness_change_, kIdleThicknessScale, 1);
 
     scrollbar->SetThumbThicknessScaleFactor(scale);
   }
 }
 
 }  // namespace cc