cros: Use SessionController for lock starting code

chrome/browser/ui/ash/session_controller_client.h

Index: chrome/browser/ui/ash/session_controller_client.h
diff --git a/chrome/browser/ui/ash/session_controller_client.h b/chrome/browser/ui/ash/session_controller_client.h
index ab9ba3f9c855aefe834891e15d4effed9a38af47..bad771a1b650b9366464487bfbd1f83e7d4bd08c 100644
--- a/chrome/browser/ui/ash/session_controller_client.h
+++ b/chrome/browser/ui/ash/session_controller_client.h
@@ -37,6 +37,13 @@ class SessionControllerClient
 
   static SessionControllerClient* Get();
 
+  // Calls SessionController to start locking ash. |callback| will be invoked
+  // to indicate whether the lock is successful. If |locked| is true, the post
+  // lock animation is finished and ash is fully locked. Otherwise, the lock
+  // is failed somehow.
+  using StartLockCallback = base::Callback<void(bool locked)>;
+  void StartLock(StartLockCallback callback);
+
   // Calls ash SessionController to run unlock animation.
   // |animation_finished_callback| will be invoked when the animation finishes.
   void RunUnlockAnimation(base::Closure animation_finished_callback);