Add metrics for interactions with the Apps Launcher promo dialog.

apps/metrics_names.h

+// 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_METRICS_NAMES_H_
+#define APPS_METRICS_NAMES_H_
+
+namespace apps {
+
+// Histogram metrics name.
+extern const char kAppLauncherPromoHistogram[];
+
+// Histogram metrics individual values.
+enum AppLauncherPromoHistogramValues {
+  APP_LAUNCHER_PROMO_ALREADY_INSTALLED,
+  APP_LAUNCHER_PROMO_SHOWN,
+  APP_LAUNCHER_PROMO_DISMISSED,
+  APP_LAUNCHER_PROMO_LEARN_MORE,
+  APP_LAUNCHER_PROMO_MAX
+};
+
+}  // namespace apps
+
+#endif  // APPS_METRICS_NAMES_H_