Cleanup mojo_shell and sample_app a bit

mojo/shell/run.cc

 // Copyright 2013 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/shell/run.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "base/message_loop/message_loop.h"
 #include "mojo/shell/app_container.h"
 #include "mojo/shell/switches.h"
 #include "url/gurl.h"
 
 namespace mojo {
 namespace shell {
 
 void Run(Context* context) {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
   if (!command_line.HasSwitch(switches::kApp)) {
     LOG(ERROR) << "No app path specified.";
+    base::MessageLoop::current()->Quit();
     return;
   }
 
   AppContainer* container = new AppContainer(context);
   container->Load(GURL(command_line.GetSwitchValueASCII(switches::kApp)));
   // TODO(abarth): Currently we leak |container|.
 }
 
 }  // namespace shell
 }  // namespace mojo