mash: remove more shell/shelf WmWindow usage.

ash/scoped_root_window_for_new_windows.h

Index: ash/scoped_root_window_for_new_windows.h
diff --git a/ash/scoped_root_window_for_new_windows.h b/ash/scoped_root_window_for_new_windows.h
index ac0946af93ea5d42e312cc04d6ccecc38efc8a3a..861f3519698e3abd9258dbfdebad5f2b1cb768f1 100644
--- a/ash/scoped_root_window_for_new_windows.h
+++ b/ash/scoped_root_window_for_new_windows.h
@@ -8,9 +8,11 @@
 #include "ash/ash_export.h"
 #include "base/macros.h"
 
-namespace ash {
+namespace aura {
+class Window;
+}
 
-class WmWindow;
+namespace ash {
 
 // Constructing a ScopedRootWindowForNewWindows allows temporarily
 // switching a target root window so that a new window gets created
@@ -19,7 +21,7 @@ class WmWindow;
 // a new window using launcher's icon.
 class ASH_EXPORT ScopedRootWindowForNewWindows {
  public:
-  explicit ScopedRootWindowForNewWindows(WmWindow* new_root);
+  explicit ScopedRootWindowForNewWindows(aura::Window* new_root);
   ~ScopedRootWindowForNewWindows();
 
  private: