Makes WorkspaceLayoutManager use ash/wm/common types

components/mus/public/cpp/lib/window_private.h

Index: components/mus/public/cpp/lib/window_private.h
diff --git a/components/mus/public/cpp/lib/window_private.h b/components/mus/public/cpp/lib/window_private.h
index 9b411f6ce7de915582de10a3acc6ae60fa730233..9fdcba663ce5db0241a8052e0302de0e2bdbaa55 100644
--- a/components/mus/public/cpp/lib/window_private.h
+++ b/components/mus/public/cpp/lib/window_private.h
@@ -25,7 +25,7 @@ class WindowPrivate {
   // Creates and returns a new Window. Caller owns the return value.
   static Window* LocalCreate();
 
-  base::ObserverList<WindowObserver>* observers() {
+  base::ObserverList<WindowObserver, true>* observers() {
     return &window_->observers_;
   }