Record some foreign fetch registration metrics.

content/browser/service_worker/service_worker_metrics.cc

Index: content/browser/service_worker/service_worker_metrics.cc
diff --git a/content/browser/service_worker/service_worker_metrics.cc b/content/browser/service_worker/service_worker_metrics.cc
index 98d494384abb69ed02d37c48be498d951b932600..d1f5af8ba866ba24093e78047f7de63243903185 100644
--- a/content/browser/service_worker/service_worker_metrics.cc
+++ b/content/browser/service_worker/service_worker_metrics.cc
@@ -384,6 +384,19 @@ void ServiceWorkerMetrics::RecordInstallEventStatus(
                             SERVICE_WORKER_ERROR_MAX_VALUE);
 }
 
+void ServiceWorkerMetrics::RecordForeignFetchRegistrationCount(
+    size_t scope_count,
+    size_t origin_count) {
+  UMA_HISTOGRAM_COUNTS_100("ServiceWorker.ForeignFetch.SubScopeCount",
+                           scope_count);

[Mark P, 2016/08/11 22:42:18]

Why is the histogram "subscopecount" yet you're using a "scope_count"?  These
things sound different to me.

[Marijn Kruisselbrink, 2016/08/12 20:33:23]

Changed it to consistently be "scope count", at least on the metrics side. After
all in the spec and rest of the implementation I also call these things "foreign
fetch scopes" and not "sub scopes". 

+  if (scope_count > 0) {
+    // Only record number of origins if service worker registered for at least
+    // one foreign fetch scope.
+    UMA_HISTOGRAM_COUNTS_100("ServiceWorker.ForeignFetch.OriginCount",
+                             origin_count);
+  }
+}
+
 void ServiceWorkerMetrics::RecordEventHandledRatio(EventType event,
                                                    size_t handled_events,
                                                    size_t fired_events) {