Close the shell when all activities are destroyed.

shell/android/main.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 "shell/android/main.h"
 
 #include <stdio.h>
 
 #include "base/android/fifo_utils.h"
 #include "base/android/jni_android.h"
@@ skipping 323 matching lines @@
       FROM_HERE, base::Bind(&StartApplicationByURL, url));
 }
 
 static void BindShell(JNIEnv* env, jclass clazz, jint shell_handle) {
   g_internal_data.Get().shell_task_runner->PostTask(
       FROM_HERE,
       base::Bind(&BindShellImpl, base::Passed(mojo::ScopedMessagePipeHandle(
                                      mojo::MessagePipeHandle(shell_handle)))));
 }
 
+static void QuitShell(JNIEnv* env, jclass jcaller) {
+  g_internal_data.Get().shell_task_runner->PostTask(
+      FROM_HERE, base::MessageLoop::QuitWhenIdleClosure());
+}
+
 bool RegisterShellService(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace shell