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..6675e63a3adbd113094511ac6fc0314be0fc9f97 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 +28,23 @@ 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) {
+    VLOG(1) << "Download file is released when byte stream arrived. Discard "
+               "the byte stream.";
+    return;
+  }
+
+  // The life cycle of download file is controlled by download item, so it's
+  // safe to use base::Unretained here.

[asanka, 2017/03/14 19:44:01]

to be precise, download_file_ is owned by download_item_ on the UI thread and is
always deleted on the FILE thread. I.e. the task that we schedule below will
always run prior to the download_file_ destructor.

[xingliu, 2017/03/14 22:48:29]

Done, polished the comment here.

+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&DownloadFile::AddByteStream, base::Unretained(download_file),
+                 base::Passed(&stream_reader), offset, length));
+}
+
 }  // namespace content