app_list: Create an app_list_switches.* to put all app list switches.

ui/app_list/app_list_switches.h

+// Copyright (c) 2012 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_APP_LIST_APP_LIST_SWITCHES_H_
+#define UI_APP_LIST_APP_LIST_SWITCHES_H_
+
+#include "ui/app_list/app_list_export.h"
+
+namespace app_list {
+namespace switches {
+
+APP_LIST_EXPORT extern const char kAppListShowAppsOnly[];
+
+}  // namespace switches
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_APP_LIST_SWITCHES_H_