Add Startup.SameVersionStartupCount histogram

components/startup_metric_utils/browser/pref_names.h

+// 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 COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_PREF_NAMES_H_
+#define COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_PREF_NAMES_H_
+
+namespace startup_metric_utils {
+namespace prefs {
+
+// Alphabetical list of preference names specific to the startup_metric_utils
+// component. Keep alphabetized, and document each in the .cc file.
+
+extern const char kLastStartupTimestamp[];
+extern const char kLastStartupVersion[];
+extern const char kSameVersionStartupCount[];
+
+}  // namespace prefs
+}  // namespace startup_metric_utils
+
+#endif  // COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_PREF_NAMES_H_