Add a new App launcher promo to the apps page / NTP.

apps/field_trial_names.h

Index: apps/field_trial_names.h
diff --git a/apps/field_trial_names.h b/apps/field_trial_names.h
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+// Copyright 2013 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 APPS_FIELD_TRIAL_NAMES_H_
+#define APPS_FIELD_TRIAL_NAMES_H_
+
+namespace apps {
+
+// Alphabetical list of field trial names specific to Apps component.
+// Keep alphabetized and document each one in the source file.
+extern const char kShowLauncherPromoOnceGroupName[];
+extern const char kResetShowLauncherPromoPrefGroupName[];
+extern const char kLauncherPromoTrialName[];
+
+}  // namespace apps
+
+#endif  // APPS_FIELD_TRIAL_NAMES_H_