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

cc/trees/layer_tree_host_impl.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_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3426 matching lines @@
       old_animation_controller->DidMouseLeave();
     }
     scroll_element_id_mouse_currently_over_ = scroll_element_id;
   }
 
   ScrollbarAnimationController* new_animation_controller =
       ScrollbarAnimationControllerForElementId(scroll_element_id);
   if (!new_animation_controller)
     return;
 
-  int scroll_layer_id = active_tree_->LayerIdByElementId(scroll_element_id);
-  for (ScrollbarLayerImplBase* scrollbar :
-       active_tree_->ScrollbarsFor(scroll_layer_id)) {
+  for (auto* scrollbar : active_tree_->ScrollbarsFor(scroll_element_id)) {
     new_animation_controller->DidMouseMoveNear(
         scrollbar->orientation(),
         DeviceSpaceDistanceToLayer(device_viewport_point, scrollbar) /
             active_tree_->device_scale_factor());
   }
 }
 
 void LayerTreeHostImpl::MouseLeave() {
   for (auto& pair : scrollbar_animation_controllers_)
     pair.second->DidMouseLeave();
@@ skipping 205 matching lines @@
   if (active_tree_->root_layer_for_testing()) {
     std::unique_ptr<base::Value> json(
         active_tree_->root_layer_for_testing()->LayerTreeAsJson());
     base::JSONWriter::WriteWithOptions(
         *json, base::JSONWriter::OPTIONS_PRETTY_PRINT, &str);
   }
   return str;
 }
 
 void LayerTreeHostImpl::RegisterScrollbarAnimationController(
-    int scroll_layer_id,
     ElementId scroll_element_id) {
   if (settings().scrollbar_animator == LayerTreeSettings::NO_ANIMATOR)
     return;
   if (ScrollbarAnimationControllerForElementId(scroll_element_id))
     return;
   scrollbar_animation_controllers_[scroll_element_id] =
-      active_tree_->CreateScrollbarAnimationController(scroll_layer_id);
+      active_tree_->CreateScrollbarAnimationController(scroll_element_id);
 }
 
 void LayerTreeHostImpl::UnregisterScrollbarAnimationController(
     ElementId scroll_element_id) {
   scrollbar_animation_controllers_.erase(scroll_element_id);
 }
 
 ScrollbarAnimationController*
 LayerTreeHostImpl::ScrollbarAnimationControllerForElementId(
     ElementId scroll_element_id) const {
@@ skipping 20 matching lines @@
   TRACE_EVENT0("cc", "LayerTreeHostImpl::SetNeedsAnimateForScrollbarAnimation");
   SetNeedsOneBeginImplFrame();
 }
 
 // TODO(danakj): Make this a return value from the Animate() call instead of an
 // interface on LTHI. (Also, crbug.com/551138.)
 void LayerTreeHostImpl::SetNeedsRedrawForScrollbarAnimation() {
   SetNeedsRedraw();
 }
 
-ScrollbarSet LayerTreeHostImpl::ScrollbarsFor(int scroll_layer_id) const {
-  return active_tree_->ScrollbarsFor(scroll_layer_id);
+ScrollbarSet LayerTreeHostImpl::ScrollbarsFor(ElementId id) const {
+  return active_tree_->ScrollbarsFor(id);
 }
 
 void LayerTreeHostImpl::AddVideoFrameController(
     VideoFrameController* controller) {
   bool was_empty = video_frame_controllers_.empty();
   video_frame_controllers_.insert(controller);
   if (current_begin_frame_tracker_.DangerousMethodHasStarted() &&
       !current_begin_frame_tracker_.DangerousMethodHasFinished())
     controller->OnBeginFrame(current_begin_frame_tracker_.Current());
   if (was_empty)
@@ skipping 542 matching lines @@
 }
 
 void LayerTreeHostImpl::UpdateScrollSourceInfo(bool is_wheel_scroll) {
   if (is_wheel_scroll)
     has_scrolled_by_wheel_ = true;
   else
     has_scrolled_by_touch_ = true;
 }
 
 }  // namespace cc