Changes how window manager obtains WindowTree from mus

components/mus/ws/window_manager_window_tree_factory_set_observer.h

Index: components/mus/ws/window_manager_window_tree_factory_set_observer.h
diff --git a/components/mus/ws/window_manager_window_tree_factory_set_observer.h b/components/mus/ws/window_manager_window_tree_factory_set_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..dd5f876d83926da5a1a867511c470cae7e7ff917
--- /dev/null
+++ b/components/mus/ws/window_manager_window_tree_factory_set_observer.h
@@ -0,0 +1,26 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_MUS_WS_WINDOW_MANAGER_WINDOW_TREE_FACTORY_SET_OBSERVER_H_
+#define COMPONENTS_MUS_WS_WINDOW_MANAGER_WINDOW_TREE_FACTORY_SET_OBSERVER_H_
+
+namespace mus {
+namespace ws {
+
+class WindowManagerWindowTreeFactory;
+
+class WindowManagerWindowTreeFactorySetObserver {
+ public:
+  // Called when the WindowTree associated with |factory| has been set
+  virtual void OnWindowManagerWindowTreeFactoryReady(
+      WindowManagerWindowTreeFactory* factory) = 0;
+
+ protected:
+  virtual ~WindowManagerWindowTreeFactorySetObserver() {}
+};
+
+}  // namespace ws
+}  // namespace mus
+
+#endif  // COMPONENTS_MUS_WS_WINDOW_MANAGER_WINDOW_TREE_FACTORY_SET_OBSERVER_H_