Add a new UMA enum to record how many download uses parallel requests

content/browser/download/parallel_download_job.cc

Index: content/browser/download/parallel_download_job.cc
diff --git a/content/browser/download/parallel_download_job.cc b/content/browser/download/parallel_download_job.cc
index 1a8b93059b30f1c12f7d4801becd6a38bda5c651..7e5221178b8f2bbb4285eb46cd1a40d748692210 100644
--- a/content/browser/download/parallel_download_job.cc
+++ b/content/browser/download/parallel_download_job.cc
@@ -69,10 +69,15 @@ void ParallelDownloadJob::Resume(bool resume_request) {
     worker.second->Resume();
 }
 
+
 int ParallelDownloadJob::GetParallelRequestCount() const {
   return GetParallelRequestCountConfig();
 }
 
+bool ParallelDownloadJob::UsesParallelRequests() const {
+  return true;
+}
+
 void ParallelDownloadJob::BuildParallelRequestAfterDelay() {
   DCHECK(workers_.empty());
   DCHECK(!requests_sent_);