Make RootScroller set the outer viewport scroll layer in the compositor

cc/trees/layer_tree_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_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 46 matching lines @@
       is_first_frame_after_commit_tracker_(-1),
       root_layer_for_testing_(nullptr),
       hud_layer_(nullptr),
       background_color_(0),
       has_transparent_background_(false),
       last_scrolled_layer_id_(Layer::INVALID_ID),
       overscroll_elasticity_layer_id_(Layer::INVALID_ID),
       page_scale_layer_id_(Layer::INVALID_ID),
       inner_viewport_scroll_layer_id_(Layer::INVALID_ID),
       outer_viewport_scroll_layer_id_(Layer::INVALID_ID),
+      root_scroller_layer_id_(Layer::INVALID_ID),
       page_scale_factor_(page_scale_factor),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       device_scale_factor_(1.f),
       painted_device_scale_factor_(1.f),
       elastic_overscroll_(elastic_overscroll),
       layers_(new OwnedLayerImplList),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
       needs_full_tree_sync_(true),
@@ skipping 345 matching lines @@
   target_tree->set_painted_device_scale_factor(painted_device_scale_factor());
   target_tree->elastic_overscroll()->PushPendingToActive();
 
   target_tree->pending_page_scale_animation_ =
       std::move(pending_page_scale_animation_);
 
   target_tree->SetViewportLayersFromIds(
       overscroll_elasticity_layer_id_, page_scale_layer_id_,
       inner_viewport_scroll_layer_id_, outer_viewport_scroll_layer_id_);
 
+  target_tree->SetRootScrollerLayerFromId(root_scroller_layer_id_);
+
   target_tree->RegisterSelection(selection_);
 
   // This should match the property synchronization in
   // LayerTreeHost::finishCommitOnImplThread().
   target_tree->set_source_frame_number(source_frame_number());
   target_tree->set_background_color(background_color());
   target_tree->set_has_transparent_background(has_transparent_background());
   target_tree->set_have_scroll_event_handlers(have_scroll_event_handlers());
   target_tree->set_event_listener_properties(
       EventListenerClass::kTouchStartOrMove,
@@ skipping 392 matching lines @@
     int overscroll_elasticity_layer_id,
     int page_scale_layer_id,
     int inner_viewport_scroll_layer_id,
     int outer_viewport_scroll_layer_id) {
   overscroll_elasticity_layer_id_ = overscroll_elasticity_layer_id;
   page_scale_layer_id_ = page_scale_layer_id;
   inner_viewport_scroll_layer_id_ = inner_viewport_scroll_layer_id;
   outer_viewport_scroll_layer_id_ = outer_viewport_scroll_layer_id;
 }
 
+void LayerTreeImpl::SetRootScrollerLayerFromId(int root_scroller_layer_id) {
+  root_scroller_layer_id_ = root_scroller_layer_id;
+}
+
 void LayerTreeImpl::ClearViewportLayers() {
   overscroll_elasticity_layer_id_ = Layer::INVALID_ID;
   page_scale_layer_id_ = Layer::INVALID_ID;
   inner_viewport_scroll_layer_id_ = Layer::INVALID_ID;
   outer_viewport_scroll_layer_id_ = Layer::INVALID_ID;
 }
 
 bool LayerTreeImpl::UpdateDrawProperties(bool update_lcd_text) {
   if (!needs_update_draw_properties_)
     return true;
@@ skipping 1236 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks and replicas.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc