Add KeepAliveStateObserver, add the Restart option

chrome/browser/lifetime/keep_alive_registry.h

 // 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_LIFETIME_KEEP_ALIVE_REGISTRY_H_
 #define CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_
 
 #include <map>
 
 #include "base/macros.h"
 #include "base/memory/singleton.h"
+#include "base/observer_list.h"
 
 enum class KeepAliveOrigin;
+enum class KeepAliveRestartOption;
+class KeepAliveStateObserver;
 
 class KeepAliveRegistry {
  public:
   static KeepAliveRegistry* GetInstance();
 
-  bool WillKeepAlive() const;
+  // Methods to query the state of the registry.
+  // TODO(dgn): This currently does not give a complete picture. It has no
+  // information about the many places that rely on IncrementKeepAliveCount and
+  // AddRefModule to keep the browser alive. Tracked by https://crbug.com/587926
+  bool IsKeepingAlive() const;
+  bool IsRestartAllowed() const;
+
+  void AddObserver(KeepAliveStateObserver* observer);
+  void RemoveObserver(KeepAliveStateObserver* observer);
 
  private:
   friend struct base::DefaultSingletonTraits<KeepAliveRegistry>;
   // Friend to be able to use Register/Unregister
   friend class ScopedKeepAlive;
+  friend std::ostream& operator<<(std::ostream& out,
+                                  const KeepAliveRegistry& registry);
 
   KeepAliveRegistry();
   ~KeepAliveRegistry();
 
   // Add/Remove entries. Do not use directly, use ScopedKeepAlive instead.
-  void Register(KeepAliveOrigin origin);
-  void Unregister(KeepAliveOrigin origin);
+  void Register(KeepAliveOrigin origin, KeepAliveRestartOption restart);
+  void Unregister(KeepAliveOrigin origin, KeepAliveRestartOption restart);
+
+  // Methods called when a specific aspect of the state of the registry changes.
+  void OnKeepingAliveChanged(bool new_keeping_alive);
+  void OnRestartAllowedChanged(bool new_restart_allowed);
 
   // Tracks the registered KeepAlives, storing the origin and the number of
   // registered KeepAlives for each.
   std::map<KeepAliveOrigin, int> registered_keep_alives_;
 
   // Total number of registered KeepAlives
   int registered_count_;
 
+  // Number of registered keep alives that have KeepAliveRestartOption::ENABLED.
+  int restart_allowed_count_;
+
+  base::ObserverList<KeepAliveStateObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(KeepAliveRegistry);
 };
 
+#ifndef NDEBUG
+std::ostream& operator<<(std::ostream& out, const KeepAliveRegistry& registry);
+#endif  // ndef NDEBUG
+
 #endif  // CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_