Cancel partial screenshot UI when lock happens.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 690ae79bb696df7fe3394cbd532ad62082c3632c..87b86c8a603c5d7026770f46863e5b1dfa26137e 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -173,6 +173,16 @@ class ASH_EXPORT Shell {
   void SetMonitorWorkAreaInsets(aura::Window* window,
                                 const gfx::Insets& insets);
 
+  // Called when the user logs in.
+  void OnLoginStateChanged(bool logged_in, bool is_guest);
+
+  // Called when the application is exiting.
+  void OnAppTerminating();
+
+  // Called when the screen is locked (after the lock window is visible) or
+  // unlocked.
+  void OnLockStateChanged(bool locked);
+
   // Initializes |launcher_|.  Does nothing if it's already initialized.
   void CreateLauncher();