Add UMA metrics to the site engagement service.

chrome/browser/engagement/site_engagement_metrics.h

+// Copyright 2015 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 CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_
+#define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_
+
+#include <map>
+
+#include "url/gurl.h"
+
+// Helper class managing the UMA histograms for the Site Engagement Service.
+class SiteEngagementMetrics {
+ public:
+  // This is used to back a UMA histogram, so it should be treated as
+  // append-only. Any new values should be inserted immediately prior to
+  // ENGAGEMENT_LAST.
+  enum EngagementType {
+    ENGAGEMENT_NAVIGATION,
+    ENGAGEMENT_KEYPRESS,
+    ENGAGEMENT_MOUSE,
+    ENGAGEMENT_LAST,
+  };
+
+  static const char kTotalEngagementHistogram[];
+  static const char kTotalOriginsHistogram[];
+  static const char kAverageEngagementHistogram[];
+  static const char kEngagementScoreHistogram[];
+  static const char kOriginsWithMaxEngagementHistogram[];
+  static const char kOriginsWithMaxDailyEngagementHistogram[];
+  static const char kPercentOriginsWithMaxEngagementHistogram[];
+  static const char kEngagementTypeHistogram[];

[calamity, 2015/10/02 03:46:28]

Can these just live in the anonymous namespace?

[dominickn, 2015/10/02 04:54:50]

No, because they're used in tests. I've privatized them.

+
+  static void RecordTotalSiteEngagement(double total_engagement);
+  static void RecordTotalOriginsEngaged(int total_origins);
+  static void RecordAverageEngagement(double average_engagement);
+  static void RecordEngagementScores(std::map<GURL, double> score_map);
+  static void RecordOriginsWithMaxEngagement(int total_origins);
+  static void RecordOriginsWithMaxDailyEngagement(int total_origins);
+  static void RecordPercentOriginsWithMaxEngagement(double percentage);
+  static void RecordEngagement(EngagementType type);
+};
+
+#endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_