Make RootScroller set the outer viewport scroll layer in the compositor

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 473 matching lines @@
         overscroll_elasticity_layer_.get() ? overscroll_elasticity_layer_->id()
                                            : Layer::INVALID_ID,
         page_scale_layer_->id(), inner_viewport_scroll_layer_->id(),
         outer_viewport_scroll_layer_.get() ? outer_viewport_scroll_layer_->id()
                                            : Layer::INVALID_ID);
     DCHECK(inner_viewport_scroll_layer_->IsContainerForFixedPositionLayers());
   } else {
     sync_tree->ClearViewportLayers();
   }
 
+  sync_tree->SetRootScrollerLayerFromId(root_scroller_layer_.get()
+                                            ? root_scroller_layer_->id()
+                                            : Layer::INVALID_ID);
+
   sync_tree->RegisterSelection(selection_);
 
   bool property_trees_changed_on_active_tree =
       sync_tree->IsActiveTree() && sync_tree->property_trees()->changed;
   // Property trees may store damage status. We preserve the sync tree damage
   // status by pushing the damage status from sync tree property trees to main
   // thread property trees or by moving it onto the layers.
   if (root_layer_ && property_trees_changed_on_active_tree) {
     if (property_trees_.sequence_number ==
         sync_tree->property_trees()->sequence_number)
@@ skipping 705 matching lines @@
     scoped_refptr<Layer> inner_viewport_scroll_layer,
     scoped_refptr<Layer> outer_viewport_scroll_layer) {
   DCHECK(!inner_viewport_scroll_layer ||
          inner_viewport_scroll_layer != outer_viewport_scroll_layer);
   overscroll_elasticity_layer_ = overscroll_elasticity_layer;
   page_scale_layer_ = page_scale_layer;
   inner_viewport_scroll_layer_ = inner_viewport_scroll_layer;
   outer_viewport_scroll_layer_ = outer_viewport_scroll_layer;
 }
 
+void LayerTreeHost::SetRootScrollerLayer(
+    scoped_refptr<Layer> root_scroller_layer) {
+  root_scroller_layer_ = root_scroller_layer;
+}
+
 void LayerTreeHost::RegisterSelection(const LayerSelection& selection) {
   if (selection_ == selection)
     return;
 
   selection_ = selection;
   SetNeedsCommit();
 }
 
 void LayerTreeHost::SetHaveScrollEventHandlers(bool have_event_handlers) {
   if (have_scroll_event_handlers_ == have_event_handlers)
@@ skipping 499 matching lines @@
   int seq_num = property_trees_.sequence_number;
   LayerTreeHostCommon::CallFunctionForEveryLayer(this, [seq_num](Layer* layer) {
     layer->set_property_tree_sequence_number(seq_num);
   });
 
   surface_id_namespace_ = proto.surface_id_namespace();
   next_surface_sequence_ = proto.next_surface_sequence();
 }
 
 }  // namespace cc