Moves maintaining root_window_for_new_windows_ to Shell

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 660b2cf8525ab570a6bee5f2c9f3fc5b20e07d5b..a838bfc30a4490eef72605e186a462c0af549583 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -319,7 +319,7 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   // Disables projection touch HUD.
   void DisableTouchHudProjection();
 
-  // Resets WmShell::GetRootWindowForNewWindows() if appropriate. This is called
+  // Resets Shell::GetRootWindowForNewWindows() if appropriate. This is called
   // during shutdown to make sure GetRootWindowForNewWindows() isn't referencing
   // this.
   void ResetRootForNewWindowsIfNecessary();