Cancel partial screenshot UI when lock happens.

ash/shell_observer.h

 // Copyright (c) 2012 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 ASH_SHELLOBSERVER_H_
 #define ASH_SHELLOBSERVER_H_
 #pragma once
 
 #include "ash/ash_export.h"
+#include "ash/system/user/login_status.h"
 
 namespace ash {
 
 class ASH_EXPORT ShellObserver {
  public:
   // Invoked after the screen's work area insets changes.
   virtual void OnMonitorWorkAreaInsetsChanged() {}
 
+  // Invoked when the user logs in.
+  virtual void OnLoginStateChanged(user::LoginStatus status) {}
+
+  // Invoked when the application is exiting.
+  virtual void OnAppTerminating() {}
+
+  // Invoked when the screen is locked (after the lock window is visible) or
+  // unlocked.
+  virtual void OnLockStateChanged(bool locked) {}
+
  protected:
   virtual ~ShellObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELLOBSERVER_H_