Nix GetRootWindowController, use RootWindowController::ForWindow.

ash/mus/top_level_window_factory.cc

Index: ash/mus/top_level_window_factory.cc
diff --git a/ash/mus/top_level_window_factory.cc b/ash/mus/top_level_window_factory.cc
index 639eb600d6a8606b0aee279ebd7e2facdf68583f..46fcc23a76ea4d0a0054e558b0ea23101557f105 100644
--- a/ash/mus/top_level_window_factory.cc
+++ b/ash/mus/top_level_window_factory.cc
@@ -72,7 +72,7 @@ RootWindowController* GetRootWindowControllerForNewTopLevelWindow(
       }
     }
   }
-  return GetRootWindowController(Shell::GetRootWindowForNewWindows());
+  return RootWindowController::ForWindow(Shell::GetRootWindowForNewWindows());
 }
 
 // Returns the bounds for the new window.