Do nothing on OnSessionStopped if ARC is being restarted.

components/arc/arc_session.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 COMPONENTS_ARC_ARC_SESSION_H_
 #define COMPONENTS_ARC_ARC_SESSION_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "base/sequenced_task_runner.h"
 #include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
 #include "components/arc/arc_bridge_service.h"
+#include "components/arc/arc_stop_reason.h"
 
 namespace arc {
 
-class ArcSessionObserver;
-
 // Starts the ARC instance and bootstraps the bridge connection.
 // Clients should implement the Delegate to be notified upon communications
 // being available.
 // The instance can be safely removed 1) before Start() is called, or 2) after
 // OnStopped() is called.
 // The number of instances must be at most one. Otherwise, ARC instances will
 // conflict.
 class ArcSession {
  public:
+  // Observer to notify events corresponding to one ARC session run.
+  class Observer {
+   public:
+    // Called when the connection with ARC instance has been established.
+    virtual void OnSessionReady() = 0;
+
+    // Called when ARC instance is stopped. This is called exactly once
+    // per instance which is Start()ed.
+    virtual void OnSessionStopped(ArcStopReason reason) = 0;
+
+   protected:
+    virtual ~Observer() = default;
+  };
+
   // Creates a default instance of ArcSession.
   static std::unique_ptr<ArcSession> Create(
       ArcBridgeService* arc_bridge_service,
       const scoped_refptr<base::TaskRunner>& blocking_task_runner);
   virtual ~ArcSession();
 
   // Starts and bootstraps a connection with the instance. The Observer's
   // OnReady() will be called if the bootstrapping is successful, or
   // OnStopped() if it is not. Start() should not be called twice or more.
   virtual void Start() = 0;
 
   // Requests to stop the currently-running instance.
   // The completion is notified via OnStopped() of the Delegate.
   virtual void Stop() = 0;
 
   // Called when Chrome is in shutdown state. This is called when the message
   // loop is already stopped, and the instance will soon be deleted.
   virtual void OnShutdown() = 0;
 
-  void AddObserver(ArcSessionObserver* observer);
-  void RemoveObserver(ArcSessionObserver* observer);
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
 
  protected:
   ArcSession();
 
-  base::ObserverList<ArcSessionObserver> observer_list_;
+  base::ObserverList<Observer> observer_list_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ArcSession);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_ARC_SESSION_H_