Do not activate system tray bubble by default

ash/aura/key_event_watcher_aura.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_AURA_KEY_EVENT_WATCHER_AURA_H_
+#define ASH_AURA_KEY_EVENT_WATCHER_AURA_H_
+
+#include <map>
+
+#include "ash/ash_export.h"
+#include "ash/common/key_event_watcher.h"
+#include "ui/events/event_handler.h"
+
+namespace ui {
+class KeyEvent;
+}
+
+namespace ash {
+
+// An EventHandler based KeyEventWatcher implementation.
+class ASH_EXPORT KeyEventWatcherAura : public KeyEventWatcher,
+                                       public ui::EventHandler {
+ public:
+  KeyEventWatcherAura();
+  ~KeyEventWatcherAura() override;
+
+  // ui::EventHandler:
+  void OnKeyEvent(ui::KeyEvent* event) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(KeyEventWatcherAura);
+};
+
+}  // namespace ash
+
+#endif  // ASH_AURA_KEY_EVENT_WATCHER_AURA_H_