cros: Use SessionController for lock starting code

ash/session/session_controller.h

Index: ash/session/session_controller.h
diff --git a/ash/session/session_controller.h b/ash/session/session_controller.h
index 5500b410eaa2aa120d25f978bbf2d7b27413b0f6..9657826c9f87fa374cfcc718db63e29946249c2e 100644
--- a/ash/session/session_controller.h
+++ b/ash/session/session_controller.h
@@ -13,7 +13,9 @@
 #include "ash/login_status.h"
 #include "ash/public/cpp/session_types.h"
 #include "ash/public/interfaces/session_controller.mojom.h"
+#include "base/callback.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 
@@ -110,6 +112,7 @@ class ASH_EXPORT SessionController
   void UpdateUserSession(mojom::UserSessionPtr user_session) override;
   void SetUserSessionOrder(
       const std::vector<uint32_t>& user_session_order) override;
+  void StartLock(const StartLockCallback& callback) override;
   void RunUnlockAnimation(const RunUnlockAnimationCallback& callback) override;
   void NotifyChromeTerminating() override;
 
@@ -131,6 +134,11 @@ class ASH_EXPORT SessionController
   // Update the |login_status_| and notify observers.
   void UpdateLoginStatus();
 
+  // Used as lock screen displayed callback of LockStateController and invoked
+  // when post lock animation finishes and ash is fully locked. It would then
+  // run |start_lock_callback_| to indicate ash is locked successfully.
+  void OnLockAnimationFinished();
+
   // Bindings for mojom::SessionController interface.
   mojo::BindingSet<mojom::SessionController> bindings_;
 
@@ -160,8 +168,13 @@ class ASH_EXPORT SessionController
   // animation starts and reset when session state is no longer LOCKED.
   bool is_unlocking_ = false;
 
+  // Pending callback for the StartLock request.
+  base::OnceCallback<void(bool)> start_lock_callback_;
+
   base::ObserverList<ash::SessionObserver> observers_;
 
+  base::WeakPtrFactory<SessionController> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(SessionController);
 };