Signin screen and locked screen status area focus advancing

ash/common/system/status_area_focus_observer.h

+// 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 ASH_COMMON_SYSTEM_STATUS_AREA_FOCUS_OBSERVER_H_
+#define ASH_COMMON_SYSTEM_STATUS_AREA_FOCUS_OBSERVER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+class ASH_EXPORT StatusAreaFocusObserver {
+ public:
+  virtual ~StatusAreaFocusObserver() {}
+
+  // On WebUILoginView, when focus enters status area widget, its focus manager
+  // will rotate focus within the widget on tab/shift-tab key events.
+  // The observer should take the focus to web contents properly.
+  virtual void OnWillReturnFocusToWebContents(bool reverse) = 0;

[xiyuan, 2016/09/12 18:19:09]

nit: OnWillReturnFocusToWebContents -> OnFocusOut

The thinking is that StatusAreaFocusObserver should be generic and does not need
to know how it is used. The comment could be something like this:
  // Invoked when the FocusManager of StatusAreaWidget has done
  // tabbing through its children.

+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_STATUS_AREA_FOCUS_OBSERVER_H_