Nix GetRootWindowController, use RootWindowController::ForWindow.

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index ec3e336d5a2a5b2e8472ba953e37e7208fb434d0..7910744e5b4252099bb9e9816ea591f93f9c4655 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -311,13 +311,13 @@ RootWindowController* RootWindowController::ForWindow(
     const aura::Window* window) {
   DCHECK(window);
   CHECK(Shell::HasInstance());
-  return GetRootWindowController(window->GetRootWindow());
+  return GetRootWindowSettings(window->GetRootWindow())->controller;
 }
 
 // static
 RootWindowController* RootWindowController::ForTargetRootWindow() {
   CHECK(Shell::HasInstance());
-  return GetRootWindowController(Shell::GetRootWindowForNewWindows());
+  return ForWindow(Shell::GetRootWindowForNewWindows());
 }
 
 void RootWindowController::ConfigureWidgetInitParamsForContainer(
@@ -1073,8 +1073,4 @@ void RootWindowController::OnTouchHudProjectionToggled(bool enabled) {
     DisableTouchHudProjection();
 }
 
-RootWindowController* GetRootWindowController(const aura::Window* root_window) {
-  return root_window ? GetRootWindowSettings(root_window)->controller : nullptr;
-}
-
 }  // namespace ash