Add new UMA stats for parallelizable download

content/browser/download/download_file.h

Index: content/browser/download/download_file.h
diff --git a/content/browser/download/download_file.h b/content/browser/download/download_file.h
index 224121a034b77a1073b4ec7923a1e9f6e94b83d4..e829c6ab3301d0befb14b0c979f94a8afa1acb5c 100644
--- a/content/browser/download/download_file.h
+++ b/content/browser/download/download_file.h
@@ -47,9 +47,9 @@ class CONTENT_EXPORT DownloadFile {
   // Upon completion, |callback| will be called on the UI
   // thread as per the comment above, passing DOWNLOAD_INTERRUPT_REASON_NONE
   // on success, or a network download interrupt reason on failure.
-  virtual void Initialize(
-      const InitializeCallback& callback,
-      const DownloadItem::ReceivedSlices& received_slices) = 0;
+  virtual void Initialize(const InitializeCallback& callback,

[xingliu, 2017/04/19 02:18:11]

FYI: sorry that I just modified this function, so you probably need to rebase.
It might cause some issue if we want to cherry pick this commit, we might need
to cherry pick another first.

[qinmin, 2017/04/19 22:42:33]

rebased in the new PS

+                          const DownloadItem::ReceivedSlices& received_slices,
+                          bool is_parallelizable) = 0;
 
   // Add a byte stream reader to write into a slice of the file, used for
   // parallel download. Called on the file thread.