Updates shadow when active window changes

components/mus/public/cpp/window_tree_connection_observer.h

Index: components/mus/public/cpp/window_tree_connection_observer.h
diff --git a/components/mus/public/cpp/window_tree_connection_observer.h b/components/mus/public/cpp/window_tree_connection_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..b29d71cd711d111cfb9239ef774d59242fcf769e
--- /dev/null
+++ b/components/mus/public/cpp/window_tree_connection_observer.h
@@ -0,0 +1,23 @@
+// Copyright 2015 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_PUBLIC_CPP_WINDOW_TREE_CONNECTION_OBSERVER_H_
+#define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_OBSERVER_H_
+
+namespace mus {
+
+class Window;
+
+class WindowTreeConnectionObserver {
+ public:
+  virtual void OnWindowTreeFocusChanged(Window* gained_focus,
+                                        Window* lost_focus) {}
+
+ protected:
+  virtual ~WindowTreeConnectionObserver() {}
+};
+
+}  // namespace mus
+
+#endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_OBSERVER_H_