Nix GetRootWindowController, use RootWindowController::ForWindow.

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index f97dce28d1bb20d25cb7955e8563fdc64a61cea0..497c942fc6031b1da60885d16941a9f6c2bc539e 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -79,7 +79,7 @@ class RootWindowLayoutManager;
 // indirectly owned and deleted by |WindowTreeHostManager|.
 // The RootWindowController for particular root window is stored in
 // its property (RootWindowSettings) and can be obtained using
-// |GetRootWindowController(aura::WindowEventDispatcher*)| function.
+// |RootWindowController::ForWindow(aura::Window*)| function.
 class ASH_EXPORT RootWindowController : public ShellObserver {
  public:
   // Enumerates the type of display. If there is only a single display then
@@ -359,12 +359,6 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   DISALLOW_COPY_AND_ASSIGN(RootWindowController);
 };
 
-// On classic ash, returns the RootWindowController for the given |root_window|.
-// On mus ash, returns the RootWindowController for the primary display.
-// See RootWindowController class comment above.
-ASH_EXPORT RootWindowController* GetRootWindowController(
-    const aura::Window* root_window);
-
 }  // namespace ash
 
 #endif  // ASH_ROOT_WINDOW_CONTROLLER_H_