Isolate initiation counts for downloads to their own histograms and improve

content/browser/download/download_stats.cc

Index: content/browser/download/download_stats.cc
diff --git a/content/browser/download/download_stats.cc b/content/browser/download/download_stats.cc
index 57fa239936df3b485736dc6bf5d896cc6eddf307..5a21fce515f3e64b73f2a702a8f3059687de10b8 100644
--- a/content/browser/download/download_stats.cc
+++ b/content/browser/download/download_stats.cc
@@ -24,6 +24,11 @@ void RecordDownloadCount(DownloadCountTypes type) {
       "Download.Counts", type, DOWNLOAD_COUNT_TYPES_LAST_ENTRY);
 }
 
+void RecordDownloadSource(DownloadInitiationSources source) {
+  UMA_HISTOGRAM_ENUMERATION(
+      "Download.Sources", source, DOWNLOAD_INITIATION_SOURCES_LAST_ENTRY);
+}
+
 void RecordDownloadCompleted(const base::TimeTicks& start, int64 download_len) {
   RecordDownloadCount(COMPLETED_COUNT);
   UMA_HISTOGRAM_LONG_TIMES("Download.Time", (base::TimeTicks::Now() - start));