Get rid of KeepAlive. Quit shell when all urls run directly by Context are closed.

mojo/shell/keep_alive.h

-// 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.
-
-#ifndef MOJO_SHELL_KEEP_ALIVE_H_
-#define MOJO_SHELL_KEEP_ALIVE_H_
-
-#include "base/basictypes.h"
-
-namespace mojo {
-namespace shell {
-
-class Context;
-class KeepAlive;
-
-class KeepAliveCounter {
- public:
-  KeepAliveCounter() : count_(0) {
-  }
- private:
-  friend class KeepAlive;
-  int count_;
-};
-
-// Instantiate this class to extend the lifetime of the thread associated
-// with |context| (i.e., the shell's UI thread). Must only be used from
-// the shell's UI thread.
-class KeepAlive {
- public:
-  explicit KeepAlive(Context* context);
-  ~KeepAlive();
-
- private:
-  static void MaybeQuit(Context* context);
-
-  Context* context_;
-
-  DISALLOW_COPY_AND_ASSIGN(KeepAlive);
-};
-
-}  // namespace shell
-}  // namespace mojo
-
-#endif  // MOJO_SHELL_KEEP_ALIVE_H_