Add BackgroundModeOptimizer that can restart the browser

chrome/browser/background/background_mode_optimizer.h

Index: chrome/browser/background/background_mode_optimizer.h
diff --git a/chrome/browser/background/background_mode_optimizer.h b/chrome/browser/background/background_mode_optimizer.h
new file mode 100644
index 0000000000000000000000000000000000000000..b2468b1fd781eeb2a07966a586de3c2d09c9f89b
--- /dev/null
+++ b/chrome/browser/background/background_mode_optimizer.h
@@ -0,0 +1,53 @@
+// Copyright 2016 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_BACKGROUND_BACKGROUND_MODE_OPTIMIZER_H_
+#define CHROME_BROWSER_BACKGROUND_BACKGROUND_MODE_OPTIMIZER_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "chrome/browser/lifetime/keep_alive_state_observer.h"
+#include "chrome/browser/ui/browser_list_observer.h"
+
+class Browser;
+
+// BackgroundModeOptimizer is responsible for applying some optimizations to
+// save resources (memory) when Chrome runs in background-only mode.
+// It tries to restart the browser to release accumulated memory when it
+// is considered non distruptive.
+class BackgroundModeOptimizer : public KeepAliveStateObserver,
+                                chrome::BrowserListObserver {
+ public:
+  ~BackgroundModeOptimizer() override;
+
+  // Creates a new BackgroundModeOptimizer. Can return null if optimizations
+  // are not supported.
+  static std::unique_ptr<BackgroundModeOptimizer> Create();
+
+  // KeepAliveStateObserver implementation
+  void OnKeepAliveStateChanged(bool is_keeping_alive) override;
+  void OnKeepAliveRestartStateChanged(bool can_restart) override;
+
+  // chrome::BrowserListObserver implementation.
+  void OnBrowserAdded(Browser* browser) override;
+
+ private:
+  friend class DummyBackgroundModeOptimizer;
+
+  BackgroundModeOptimizer();
+
+  // Calls DoRestart() if the current state of the process allows it.
+  void TryBrowserRestart();
+
+  // Stop the browser and restart it in background mode.
+  // Virtual for testing purposes.
+  virtual void DoRestart();
+
+  bool browser_was_added_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackgroundModeOptimizer);
+};
+
+#endif  // CHROME_BROWSER_BACKGROUND_BACKGROUND_MODE_OPTIMIZER_H_