Cleanup: Pull some browser keep alive functions into its own file.

chrome/browser/lifetime/browser_keep_alive.h

+// Copyright 2015 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 CHROME_BROWSER_LIFETIME_BROWSER_KEEP_ALIVE_H_
+#define CHROME_BROWSER_LIFETIME_BROWSER_KEEP_ALIVE_H_
+
+#include "base/macros.h"
+
+namespace browser_lifetime {

[sky, 2015/10/07 17:27:24]

I don't think I would go with any namespace here. But I'm fine with this if you
want it.

+
+// A class that can be put in a scoped_ptr to represent a "keep alive" resource.
+// Prefer this over IncrementKeepAliveCount() / DecrementKeepAliveCount()
+// whenever possible.
+class ScopedKeepAlive {
+ public:
+  ScopedKeepAlive();
+  ~ScopedKeepAlive();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedKeepAlive);
+};
+
+// Tells the BrowserList to keep the application alive after the last Browser
+// closes. This is implemented as a count, so callers should pair their calls
+// to IncrementKeepAliveCount() with matching calls to DecrementKeepAliveCount()
+// when they no
+// longer need to keep the application running.
+void IncrementKeepAliveCount();

[sky, 2015/10/07 17:27:24]

WDYT of moving these to ScopedKeepAlive, making them private state and friending
the places that are hard? That way we shouldn't get new uses.

+
+// Stops keeping the application alive after the last Browser is closed.
+// Should match a previous call to IncrementKeepAliveCount().
+void DecrementKeepAliveCount();
+
+// Returns true if application will continue running after the last Browser
+// closes.
+bool WillKeepAlive();
+
+// Disable browser shutdown for unit tests.
+void DisableShutdownForTesting(bool disable_shutdown_for_testing);
+
+}  // namespace browser_lifetime
+
+#endif  // CHROME_BROWSER_LIFETIME_BROWSER_KEEP_ALIVE_H_
+