Isolate initiation counts for downloads to their own histograms and improve

chrome/browser/download/download_resource_throttle.cc

Index: chrome/browser/download/download_resource_throttle.cc
diff --git a/chrome/browser/download/download_resource_throttle.cc b/chrome/browser/download/download_resource_throttle.cc
index 87d41dc7939feb8e815e525c660bc0e22139db90..d6f9940d3f81fac3f6ff2d43609180fd2f12a8e6 100644
--- a/chrome/browser/download/download_resource_throttle.cc
+++ b/chrome/browser/download/download_resource_throttle.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/download/download_resource_throttle.h"
 
 #include "base/bind.h"
+#include "chrome/browser/download/download_util.h"
 #include "content/public/browser/resource_throttle_controller.h"
 
 DownloadResourceThrottle::DownloadResourceThrottle(
@@ -43,8 +44,11 @@ void DownloadResourceThrottle::ContinueDownload(bool allow) {
 
   if (request_deferred_) {
     if (allow) {
+      download_util::RecordDownloadSource(
+          download_util::INITIATED_BY_NAVIGATION);
       controller()->Resume();
     } else {
+      download_util::RecordDownloadCount(download_util::BLOCKED_BY_THROTTLING);
       controller()->Cancel();
     }
   }