Add lock pod animation on unlock.

ash/wm/session_state_controller.h

Index: ash/wm/session_state_controller.h
diff --git a/ash/wm/session_state_controller.h b/ash/wm/session_state_controller.h
index fe5664b012d3ca1be9d55881865dde73bd67decd..2a94bc81845b81c8f8d383baac44fe4fa38948d5 100644
--- a/ash/wm/session_state_controller.h
+++ b/ash/wm/session_state_controller.h
@@ -131,6 +131,11 @@ class ASH_EXPORT SessionStateController : public aura::RootWindowObserver,
   // Displays the shutdown animation and requests shutdown when it's done.
   virtual void RequestShutdown() = 0;
 
+  // Called when ScreenLocker is ready to close, but not yet destroyed.
+  // Can be used to display "hiding" animations on unlock.
+  // |callback| will be called when all animations are done.
+  virtual void OnLockScreenHide(base::Callback<void(void)>& callback) = 0;
+
  protected:
   friend class test::PowerButtonControllerTest;