ash: Rename SessionController to SessionControllerImpl

No functionality change. Just renaming so that SessionContrller/Client
could be used to replace mojom::SessionContrller/Client.

Bug: 958214
Change-Id: I7fb597f955073564fb85c8a55e1c3aacc8cc4fe4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597201
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657021}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index 65fd9ff..251acab 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -11,7 +11,7 @@
 #include "ash/login/ui/login_data_dispatcher.h"
 #include "ash/public/cpp/ash_pref_names.h"
 #include "ash/root_window_controller.h"
-#include "ash/session/session_controller.h"
+#include "ash/session/session_controller_impl.h"
 #include "ash/shelf/login_shelf_view.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shelf/shelf_widget.h"