Range request support for parallel download in DownloadRequestCore.

content/public/browser/download_save_info.h

Index: content/public/browser/download_save_info.h
diff --git a/content/public/browser/download_save_info.h b/content/public/browser/download_save_info.h
index 69893f4bbd601f76f738644d3c8546d6e57ab8a5..13977a0e3d2491024e071a023071de9eded824ab 100644
--- a/content/public/browser/download_save_info.h
+++ b/content/public/browser/download_save_info.h
@@ -22,6 +22,9 @@ namespace content {
 // name, |offset| is set to the point where we left off, and |hash_state| will
 // hold the state of the hash algorithm where we left off.
 struct CONTENT_EXPORT DownloadSaveInfo {
+  // The default value for |length|.
+  static const int kLengthUnknown;

[David Trainor- moved to gerrit, 2017/02/01 07:14:36]

I don't feel strongly, but would a name that more represents 'whole file' be
better than 'unknown'?

[xingliu, 2017/02/01 20:25:46]

Changed to kLengthFullContent;

+
   DownloadSaveInfo();
   ~DownloadSaveInfo();
   DownloadSaveInfo(DownloadSaveInfo&& that);
@@ -41,6 +44,11 @@ struct CONTENT_EXPORT DownloadSaveInfo {
   // The file offset at which to start the download.  May be 0.
   int64_t offset;
 
+  // The length of the bytes from |offset|. Set to |kLengthUnknown| by default.
+  // Ask to retrieve segment of the download file when length is greater than 0.

[David Trainor- moved to gerrit, 2017/02/01 07:14:36]

Nit, just curious about whether or not 0 is a valid length.

[xingliu, 2017/02/01 20:25:46]

Yes, this is something weird, changed the const to 0.

When it's 0, it doesn't make sense to send a request or save 0 bytes on disk, so
it's probably ok for 0 to represent the whole file.

+  // Request the whole file when length is |kLengthUnknown|.
+  int64_t length;
+
   // The state of the hash. If specified, this hash state must indicate the
   // state of the partial file for the first |offset| bytes.
   std::unique_ptr<crypto::SecureHash> hash_state;