Makes ash/mus use RootWindowControllerCommon

ash/mus/bridge/wm_window_mus.h

Index: ash/mus/bridge/wm_window_mus.h
diff --git a/ash/mus/bridge/wm_window_mus.h b/ash/mus/bridge/wm_window_mus.h
index cfd11b260c25852048aba43435a88ce58e0d3e3f..29ad94c13361025ed54df8faa776229605d6765b 100644
--- a/ash/mus/bridge/wm_window_mus.h
+++ b/ash/mus/bridge/wm_window_mus.h
@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "ash/common/shell_window_ids.h"
 #include "ash/common/wm_window.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
@@ -224,7 +225,7 @@ class WmWindowMus : public WmWindow, public ::mus::WindowObserver {
 
   // The shell window id of this window. Shell window ids are defined in
   // ash/common/shell_window_ids.h.
-  int shell_window_id_ = -1;
+  int shell_window_id_ = kShellWindowId_Invalid;
 
   std::unique_ptr<wm::WindowState> window_state_;