mash: Run pre-unlock animation via SessionController

ash/session/session_state_observer.h

Index: ash/session/session_state_observer.h
diff --git a/ash/session/session_state_observer.h b/ash/session/session_state_observer.h
index 74d5afc1679dc7278eda9d618d1289a6954c512b..736679b885b8b74f6baca77e632602791a96c8e5 100644
--- a/ash/session/session_state_observer.h
+++ b/ash/session/session_state_observer.h
@@ -15,6 +15,7 @@ namespace ash {
 
 enum class LoginStatus;
 
+// TODO(xiyuan): Rename to On*Changed().
 class ASH_EXPORT SessionStateObserver {
  public:
   // Called when active user has changed.
@@ -32,6 +33,9 @@ class ASH_EXPORT SessionStateObserver {
   // Called when the login status is changed. |login_status| is the new status.
   virtual void LoginStatusChanged(LoginStatus login_status) {}
 
+  // Called when the lock state is changed. |locked| is the current lock stated.
+  virtual void LockStateChanged(bool locked) {}
+
  protected:
   virtual ~SessionStateObserver() {}
 };