Do not activate system tray bubble by default

ash/common/key_event_watcher.h

Index: ash/common/key_event_watcher.h
diff --git a/ash/common/key_event_watcher.h b/ash/common/key_event_watcher.h
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+++ b/ash/common/key_event_watcher.h
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+// 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_KEY_EVENT_WATCHER_H_
+#define ASH_COMMON_KEY_EVENT_WATCHER_H_
+
+#include <map>
+
+#include "ash/ash_export.h"
+#include "base/callback.h"
+#include "base/macros.h"
+#include "ui/base/accelerators/accelerator.h"
+
+namespace ui {
+class KeyEvent;
+}
+
+namespace ash {
+
+// This class watches the key event given in the form of accelerator
+// and calls the registered callback.
+class ASH_EXPORT KeyEventWatcher {
+ public:
+  using KeyEventCallback = base::Callback<void(const ui::KeyEvent&)>;
+
+  KeyEventWatcher();
+  virtual ~KeyEventWatcher();
+
+  // Add a callback that is called when the accelerator |accel| is
+  // matched. The key event will be consumed if a matching accelerator
+  // is found.
+  void AddKeyEventCallback(const ui::Accelerator& accel,
+                           const KeyEventCallback& callback);
+
+ protected:
+  // Finds and calls the registered callback whose accelerator matches
+  // the |event|. Returns false if no accelerator is matched.
+  bool HandleKeyEvent(const ui::KeyEvent& event);
+
+ private:
+  std::map<ui::Accelerator, KeyEventCallback> callback_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeyEventWatcher);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_KEY_EVENT_WATCHER_H_