Add new UMA stats for parallelizable download

content/browser/download/download_job.h

Index: content/browser/download/download_job.h
diff --git a/content/browser/download/download_job.h b/content/browser/download/download_job.h
index 0998cea50072d471842b1fe4fad076d297fce400..2f12b18b1f098b820cd04eb004dec6df2b6c8332 100644
--- a/content/browser/download/download_job.h
+++ b/content/browser/download/download_job.h
@@ -40,8 +40,9 @@ class CONTENT_EXPORT DownloadJob {
   // WebContents.
   virtual WebContents* GetWebContents() const = 0;
 
-  // Returns whether the download uses parallel requests.
-  virtual bool UsesParallelRequests() const;
+  // Returns whether the download is parallelizable. The download may not send
+  // parallel requests as it can be disabled through flags.
+  virtual bool IsParallelizable() const;
 
   // Cancel a particular request starts from |offset|, while the download is not
   // canceled. Used in parallel download.