Add UMA metrics to the site engagement service.

chrome/browser/engagement/site_engagement_metrics.cc

+// 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.
+
+#include "chrome/browser/engagement/site_engagement_metrics.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/metrics/sparse_histogram.h"
+
+void SiteEngagementMetrics::RecordTotalCumulativeSiteEngagement(
+    double total_engagement) {
+  UMA_HISTOGRAM_COUNTS_100("SiteEngagementService.CumulativeTotal",
+                           total_engagement);
+}
+
+void SiteEngagementMetrics::RecordTotalOriginsEngaged(int num_origins) {
+  UMA_HISTOGRAM_COUNTS_100("SiteEngagementService.OriginsEngaged", num_origins);
+}
+
+void SiteEngagementMetrics::RecordEngagementPerOrigin(
+    std::map<GURL, double> score_map) {
+  for (const auto& value: score_map) {
+    UMA_HISTOGRAM_COUNTS_100("SiteEngagementService.EngagementPerOrigin",
+                             value.second);
+  }
+}
+
+void SiteEngagementMetrics::RecordOriginsWithMaxEngagement(int total_origins) {
+  UMA_HISTOGRAM_COUNTS_100("SiteEngagementService.OriginsWithMaxEngagement",
+                           total_origins);
+}
+
+void SiteEngagementMetrics::RecordOriginsWithMaxDailyEngagement(
+    int total_origins) {
+  UMA_HISTOGRAM_COUNTS_100(
+      "SiteEngagementService.OriginsWithMaxDailyEngagement", total_origins);
+}
+
+void SiteEngagementMetrics::RecordEngagement(EngagementType type) {
+  switch (type) {
+    case ENGAGEMENT_NAVIGATION:
+      UMA_HISTOGRAM_SPARSE_SLOWLY("SiteEngagementService.EngagementType",

[calamity, 2015/09/25 07:08:33]

So what does SPARSE_SLOWLY do?

[dominickn, 2015/09/28 03:34:50]

asvitkine recommend that I use it instead of UMA_HISTOGRAM_CUSTOM_ENUMERATION in
an app banner CL a couple of months ago, so I stuck with it here for the enum
histogram.

[calamity, 2015/09/28 07:33:47]

Acknowledged.

+          ENGAGEMENT_NAVIGATION);
+      break;
+    case ENGAGEMENT_KEYPRESS:
+      UMA_HISTOGRAM_SPARSE_SLOWLY("SiteEngagementService.EngagementType",

[calamity, 2015/09/25 07:08:33]

Pull into a local constant.

[dominickn, 2015/09/28 03:34:50]

Done.

+                                  ENGAGEMENT_KEYPRESS);
+      break;
+    case ENGAGEMENT_MOUSE:
+      UMA_HISTOGRAM_SPARSE_SLOWLY("SiteEngagementService.EngagementType",
+                                  ENGAGEMENT_MOUSE);
+      break;
+    default:
+      NOTREACHED() << "Invalid type passed to RecordUserInput().";
+      break;
+  }
+}