Updates shadow when active window changes

mash/wm/shadow_controller.h

Index: mash/wm/shadow_controller.h
diff --git a/mash/wm/shadow_controller.h b/mash/wm/shadow_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..cc11f4fd4858508f8f4fc23e1c2e4e18fc129669
--- /dev/null
+++ b/mash/wm/shadow_controller.h
@@ -0,0 +1,44 @@
+// 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 MASH_WM_SHADOW_CONTROLLER_H_
+#define MASH_WM_SHADOW_CONTROLLER_H_
+
+#include "base/basictypes.h"
+#include "components/mus/public/cpp/window_observer.h"
+#include "components/mus/public/cpp/window_tree_connection_observer.h"
+
+namespace mus {
+class WindowTreeConnection;
+}
+
+namespace mash {
+namespace wm {
+
+class ShadowController : public mus::WindowTreeConnectionObserver,
+                         public mus::WindowObserver {
+ public:
+  explicit ShadowController(mus::WindowTreeConnection* window_tree);
+  ~ShadowController() override;
+
+ private:
+  void SetActiveWindow(mus::Window* window);
+
+  // mus::WindowTreeConnectionObserver:
+  void OnWindowTreeFocusChanged(mus::Window* gained_focus,
+                                mus::Window* lost_focus) override;
+
+  // mus::WindowObserver:
+  void OnWindowDestroying(mus::Window* window) override;
+
+  mus::WindowTreeConnection* window_tree_;
+  mus::Window* active_window_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShadowController);
+};
+
+}  // namespace wm
+}  // namespace mash
+
+#endif  // MASH_WM_SHADOW_CONTROLLER_H_