Reset the root layer on the compositor when recreating a root layer.

ui/compositor/layer_owner.cc

 // Copyright (c) 2012 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 "ui/compositor/layer_owner.h"
 
 #include "ui/compositor/layer_owner_delegate.h"
 
 namespace ui {
 
@@ skipping 48 matching lines @@
   // Migrate all the child layers over to the new layer. Copy the list because
   // the items are removed during iteration.
   std::vector<ui::Layer*> children_copy = old_layer->children();
   for (std::vector<ui::Layer*>::const_iterator it = children_copy.begin();
        it != children_copy.end();
        ++it) {
     ui::Layer* child = *it;
     new_layer->Add(child);
   }
 
+  ui::Layer* root_layer = old_layer.get();
+  while (root_layer->parent())
+    root_layer = root_layer->parent();

[sadrul, 2015/03/06 14:33:49]

You don't actually need to walk up to the root, right? You can just do:
  bool is_root = !old_layer->parent();
  if (is_root && ...)
    ...

[bruthig, 2015/03/06 15:20:41]

Done.

+
+  // If old_layer was the layer tree root then we need to move the Compositor
+  // over to the new root.
+  if (root_layer == old_layer.get() && old_layer->GetCompositor())
+    old_layer->GetCompositor()->SetRootLayer(new_layer);
+
   // Install the delegate last so that the delegate isn't notified as we copy
   // state to the new layer.
   new_layer->set_delegate(old_delegate);
 
   if (layer_owner_delegate_)
     layer_owner_delegate_->OnLayerRecreated(old_layer.get(), new_layer);
 
   return old_layer.Pass();
 }
 
 void LayerOwner::DestroyLayer() {
   layer_ = NULL;
   layer_owner_.reset();
 }
 
 bool LayerOwner::OwnsLayer() const {
   return !!layer_owner_;
 }
 
 }  // namespace ui