[cc] Change semantics of fixed-pos container layer

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 1138 matching lines @@
       EventListenerClass::kTouchEndOrCancel,
       event_listener_properties(EventListenerClass::kTouchEndOrCancel));
 
   if (page_scale_layer_ && inner_viewport_scroll_layer_) {
     tree_impl->SetViewportLayersFromIds(
         overscroll_elasticity_layer_ ? overscroll_elasticity_layer_->id()
                                      : Layer::INVALID_ID,
         page_scale_layer_->id(), inner_viewport_scroll_layer_->id(),
         outer_viewport_scroll_layer_ ? outer_viewport_scroll_layer_->id()
                                      : Layer::INVALID_ID);
-    DCHECK(inner_viewport_scroll_layer_->IsContainerForFixedPositionLayers());
+    DCHECK(page_scale_layer_->IsContainerForFixedPositionLayers());

[bokan, 2017/04/26 21:17:56]

I think this DCHECK should be for the outer container layer.

   } else {
     tree_impl->ClearViewportLayers();
   }
 
   tree_impl->RegisterSelection(selection_);
 
   bool property_trees_changed_on_active_tree =
       tree_impl->IsActiveTree() && tree_impl->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
@@ skipping 271 matching lines @@
 void LayerTreeHost::SetNeedsDisplayOnAllLayers() {
   for (auto* layer : *this)
     layer->SetNeedsDisplay();
 }
 
 void LayerTreeHost::SetHasCopyRequest(bool has_copy_request) {
   has_copy_request_ = has_copy_request;
 }
 
 }  // namespace cc