Make DownloadFileImpl handle multiple byte streams.

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 0e34ab24362d3c2d48af5722e5df7e8291e31e26..c155cb216ee8c8385b094ad9d0156afeb67c9119 100644
--- a/content/browser/download/download_file.h
+++ b/content/browser/download/download_file.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include <memory>
 #include <string>
 
 #include "base/callback_forward.h"
@@ -18,6 +19,8 @@ class GURL;
 
 namespace content {
 
+class ByteStreamReader;
+
 // These objects live exclusively on the file thread and handle the writing
 // operations for one download. These objects live only for the duration that
 // the download is 'in progress': once the download has been completed or
@@ -45,6 +48,11 @@ class CONTENT_EXPORT DownloadFile {
   // on success, or a network download interrupt reason on failure.
   virtual void Initialize(const InitializeCallback& callback) = 0;
 
+  // Add a byte stream reader to write into a slice of the file, used for
+  // parallel download. Called on the file thread.
+  virtual void AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
+                             int64_t offset) = 0;
+
   // Rename the download file to |full_path|.  If that file exists
   // |full_path| will be uniquified by suffixing " (<number>)" to the
   // file name before the extension.