Implement media playing engagement detection for 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 "base/gtest_prod_util.h"
 #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_TOUCH_GESTURE,
     ENGAGEMENT_WHEEL,
+    ENGAGEMENT_MEDIA_HIDDEN,
+    ENGAGEMENT_MEDIA_VISIBLE,
     ENGAGEMENT_LAST,
   };
 
   static void RecordTotalSiteEngagement(double total_engagement);
   static void RecordTotalOriginsEngaged(int total_origins);
   static void RecordMeanEngagement(double mean_engagement);
   static void RecordMedianEngagement(double median_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);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementServiceTest, CheckHistograms);
   FRIEND_TEST_ALL_PREFIXES(SiteEngagementHelperTest,
                            MixedInputEngagementAccumulation);
   static const char kTotalEngagementHistogram[];
   static const char kTotalOriginsHistogram[];
   static const char kMeanEngagementHistogram[];
   static const char kMedianEngagementHistogram[];
   static const char kEngagementScoreHistogram[];
   static const char kOriginsWithMaxEngagementHistogram[];
   static const char kOriginsWithMaxDailyEngagementHistogram[];
   static const char kPercentOriginsWithMaxEngagementHistogram[];
   static const char kEngagementTypeHistogram[];
 };
 
 #endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_METRICS_H_