Re-reland: chromeos: Fix shelf appearing at login screen under mash

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 d97bc6bb75e10d50a9aa74e4b087c0772c3108cd..c2d22c9061109c328e33e528dc366ddce603aae9 100644
--- a/chrome/browser/ui/ash/session_controller_client.h
+++ b/chrome/browser/ui/ash/session_controller_client.h
@@ -50,6 +50,9 @@ class SessionControllerClient
   static void DoSwitchActiveUser(const AccountId& account_id);
   static void DoCycleActiveUser(bool next_user);
 
+  // Flushes the mojo pipe to ash.
+  static void FlushForTesting();
+
  private:
   // Connects or reconnects to the |session_controller_| interface and set
   // this object as its client.