Change FocusSynchronizer to maintain active focus client and window.

ui/aura/mus/focus_synchronizer_observer.h

Index: ui/aura/mus/focus_synchronizer_observer.h
diff --git a/ui/aura/mus/focus_synchronizer_observer.h b/ui/aura/mus/focus_synchronizer_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..34d30b0724d1b86c4dff3787e29d05330afe44b0
--- /dev/null
+++ b/ui/aura/mus/focus_synchronizer_observer.h
@@ -0,0 +1,34 @@
+// Copyright 2017 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 UI_AURA_MUS_FOCUS_SYNCHRONIZER_OBSERVER_H_
+#define UI_AURA_MUS_FOCUS_SYNCHRONIZER_OBSERVER_H_
+
+#include "ui/aura/aura_export.h"
+
+namespace aura {
+class Window;
+
+namespace client {
+class FocusClient;
+}
+
+// FocusSynchronizerObserver gets notified when the active focus client and the
+// window it's associated with (active focus client root) maintained by
+// FocusSynchronizer changed. To get notified when the actual focused window
+// gets changed, use FocusChangeObserver instead.
+class AURA_EXPORT FocusSynchronizerObserver {
+ public:
+  // Called from FocusSynchronizer::SetActiveFocusClient() to notify its
+  // observers of active focus client and active focus client root changes.
+  virtual void OnActiveFocusClientChanged(client::FocusClient* focus_client,
+                                          Window* focus_client_root) {}
+
+ protected:
+  virtual ~FocusSynchronizerObserver() {}

[sadrul, 2017/03/28 15:03:23]

I think this can just be public

[riajiang, 2017/03/28 22:07:27]

But the current pattern of other observer classes is putting dtor in protected?

[sadrul, 2017/03/29 16:13:19]

Yes. I can't think of a good reason for doing this though. You can keep it as it
is, or move it to public. Upto you.

[riajiang, 2017/03/29 17:27:35]

I think I'll keep it here to be consistent for now.

+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_MUS_FOCUS_SYNCHRONIZER_OBSERVER_H_