Glue parallel download job and download file together.

content/browser/download/download_job.cc

Index: content/browser/download/download_job.cc
diff --git a/content/browser/download/download_job.cc b/content/browser/download/download_job.cc
index 4da7eb429ae6eca4a6b880e8924dbe5f79e7a054..712cc2b5d02d2ffc9fcaf04f016c26e21f4e6b9a 100644
--- a/content/browser/download/download_job.cc
+++ b/content/browser/download/download_job.cc
@@ -4,7 +4,10 @@
 
 #include "content/browser/download/download_job.h"
 
+#include "base/bind_helpers.h"
+#include "content/browser/download/download_file.h"
 #include "content/browser/download/download_item_impl.h"
+#include "content/public/browser/browser_thread.h"
 
 namespace content {
 
@@ -25,4 +28,20 @@ void DownloadJob::StartDownload() const {
   download_item_->StartDownload();
 }
 
+void DownloadJob::AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
+                                int64_t offset,
+                                int64_t length) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DownloadFile* download_file = download_item_->download_file_.get();
+  if (!download_file)
+    return;

[David Trainor- moved to gerrit, 2017/03/14 17:59:10]

When do we expect this to happen?

[xingliu, 2017/03/14 18:26:31]

Done, added a VLOG.

download_file is invalidated when DownloadItemImpl calls ReleaseDownloadFile.
 
It happens if the download is interrupted or complete, or restart a download
after user cancel the download.

The AddByteStream still may be called since the server response may arrive later
after something goes wrong or the original request complete the download.

We probably need to test this when put everything together. A cancel call may be
needed to kill the url_request in job class.

[David Trainor- moved to gerrit, 2017/03/17 07:15:27]

sg.  add a TODO to investigate/file a bug?

[xingliu, 2017/03/17 19:08:25]

Done.

+
+  // The life cycle of download file is controlled by download item, so it's
+  // safe to use base::Unretained here.
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&DownloadFile::AddByteStream, base::Unretained(download_file),
+                 base::Passed(&stream_reader), offset, length));
+}
+
 }  // namespace content