Show overlay displaying the state of all sticky keys when it is enabled.

ash/sticky_keys/sticky_keys_constants.h

+// Copyright 2014 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_STICKY_KEYS_STICKY_KEYS_CONSTANTS_H_
+#define ASH_STICKY_KEYS_STICKY_KEYS_CONSTANTS_H_
+
+namespace ash {
+
+// Modifiers supported for sticky keys.
+enum StickyKeyModifier {
+  STICKY_KEY_SHIFT,
+  STICKY_KEY_ALT,
+  STICKY_KEY_CONTROL,
+  STICKY_KEY_SEARCH
+};
+
+// State of an individual modifier key.
+enum StickyKeyState {
+  // The sticky key is disabled. Incoming non-modifier key events are not
+  // affected.
+  STICKY_KEY_STATE_DISABLED,
+  // The sticky key is enabled. Incoming non-modifier key down events are
+  // modified. After that, sticky key state become DISABLED.

[James Cook, 2014/01/14 00:59:03]

become -> becomes

[Tim Song, 2014/01/14 03:01:10]

Done.

+  STICKY_KEY_STATE_ENABLED,
+  // The sticky key is locked. All incoming non modifier key down events are
+  // modified.
+  STICKY_KEY_STATE_LOCKED,
+};
+
+}  // ash
+
+#endif  // ASH_WM_STICKY_KEYS_CONTROLLER_H_