Update setting of Compositor on new 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 34 matching lines @@
   new_layer->set_name(old_layer->name());
   new_layer->SetFillsBoundsOpaquely(old_layer->fills_bounds_opaquely());
   new_layer->SetFillsBoundsCompletely(old_layer->FillsBoundsCompletely());
   new_layer->SetSubpixelPositionOffset(old_layer->subpixel_position_offset());
   if (old_layer->type() == LAYER_SOLID_COLOR)
     new_layer->SetColor(old_layer->GetTargetColor());
   SkRegion* alpha_shape = old_layer->alpha_shape();
   if (alpha_shape)
     new_layer->SetAlphaShape(make_scoped_ptr(new SkRegion(*alpha_shape)));
 
-  // Install new layer as a sibling of the old layer, stacked below it.
   if (old_layer->parent()) {
+    // Install new layer as a sibling of the old layer, stacked below it.
     old_layer->parent()->Add(new_layer);
     old_layer->parent()->StackBelow(new_layer, old_layer.get());
+  } else if (old_layer->GetCompositor()) {
+    // If old_layer was the layer tree root then we need to move the Compositor
+    // over to the new root.
+    old_layer->GetCompositor()->SetRootLayer(new_layer);
   }
 
   // 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);
   }
 
-  // If old_layer was the layer tree root then we need to move the Compositor
-  // over to the new root.
-  const bool is_root = !old_layer->parent();
-  if (is_root && 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