Fix destruction tests.

mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.cc

 // Copyright 2014 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 "mojo/services/public/cpp/view_manager/lib/view_manager_synchronizer.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "mojo/public/cpp/application/connect.h"
 #include "mojo/public/interfaces/service_provider/service_provider.mojom.h"
@@ skipping 586 matching lines @@
     ViewTreeNodePrivate(new_parent).LocalAddChild(node);
   else
     ViewTreeNodePrivate(old_parent).LocalRemoveChild(node);
 }
 
 void ViewManagerSynchronizer::OnNodeDeleted(uint32_t node_id,
                                             uint32_t server_change_id) {
   next_server_change_id_ = server_change_id + 1;
 
   ViewTreeNode* node = view_manager()->GetNodeById(node_id);
-  if (node)
+  if (node) {
+    if (view_manager()->tree() == node)
+      ViewManagerPrivate(view_manager()).set_root(NULL);
     ViewTreeNodePrivate(node).LocalDestroy();
+  }
 }
 
 void ViewManagerSynchronizer::OnNodeViewReplaced(uint32_t node_id,
                                                  uint32_t new_view_id,
                                                  uint32_t old_view_id) {
   ViewTreeNode* node = view_manager()->GetNodeById(node_id);
   View* new_view = view_manager()->GetViewById(new_view_id);
   if (!new_view && new_view_id != 0) {
     // This client wasn't aware of this View until now.
     new_view = ViewPrivate::LocalCreate();
@@ skipping 33 matching lines @@
 void ViewManagerSynchronizer::RemoveFromPendingQueue(
     ViewManagerTransaction* transaction) {
   DCHECK_EQ(transaction, pending_transactions_.front());
   pending_transactions_.erase(pending_transactions_.begin());
   if (pending_transactions_.empty() && !changes_acked_callback_.is_null())
     changes_acked_callback_.Run();
 }
 
 }  // namespace view_manager
 }  // namespace mojo