Makes it so a node can only the root of one connection at a time

mojo/services/public/cpp/view_manager/lib/view_manager_client_impl.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_client_impl.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "mojo/public/cpp/application/application_connection.h"
 #include "mojo/public/cpp/application/connect.h"
@@ skipping 460 matching lines @@
                    Id node_id,
                    ViewManagerClientImpl* client)
       : ViewManagerTransaction(client),
         url_(url),
         node_id_(node_id) {}
   virtual ~EmbedTransaction() {}
 
  private:
   // Overridden from ViewManagerTransaction:
   virtual void DoCommit() OVERRIDE {
+    GetAndAdvanceNextServerChangeId();
     service()->Embed(url_, node_id_, ActionCompletedCallback());
   }
   virtual void DoActionCompleted(bool success) OVERRIDE {
     // TODO(beng): recovery?
   }
 
   const String url_;
   const Id node_id_;
 
   DISALLOW_COPY_AND_ASSIGN(EmbedTransaction);
@@ skipping 417 matching lines @@
 
 // static
 void ViewManager::ConfigureIncomingConnection(
     ApplicationConnection* connection,
     ViewManagerDelegate* delegate) {
   connection->AddService<ViewManagerClientImpl>(delegate);
 }
 
 }  // namespace view_manager
 }  // namespace mojo