Add Startup.SameVersionStartupCount histogram

components/startup_metric_utils/browser/pref_names.cc

+// 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.
+
+#include "components/startup_metric_utils/browser/pref_names.h"
+
+namespace startup_metric_utils {
+namespace prefs {
+
+// Time of the last startup stored as an int64.
+const char kLastStartupTimestamp[] = "startup_metric.last_startup_timestamp";
+
+// Version of the product in the startup preceding this one as reported by
+// version_info.h.
+const char kLastStartupVersion[] = "startup_metric.last_startup_version";
+
+// Number of startups previously seen with kLastStartupVersion.
+const char kSameVersionStartupCount[] =
+    "startup_metric.same_version_startup_count";
+
+}  // namespace prefs
+}  // namespace startup_metric_utils