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 Chrome startup stored as an int64.

[fdoray, 2016/01/22 16:08:54]

Is it ok to use Chrome in comments considering that startup_metric_utils is also
used by components/html_viewer?

[gab, 2016/01/22 16:51:44]

Good point, removed and also adapted existing comments (still a few instances
remaining in the .cc file around the 7-minutes stuff -- probably a good cleanup
for your pending 7minutes CL).

+const char kLastStartupTimestamp[] = "startup_metric.last_startup_timestamp";
+
+// Version of Chrome in the startup preceding this one.
+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