Downloads: replace BrowserThread::FILE with task scheduler.

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 5bd23a4291bf7355f6158cbe798f70fd7d22006a..3771700ef6ade945187d5e85adbc9090083b9b5d 100644
--- a/content/browser/download/download_job.cc
+++ b/content/browser/download/download_job.cc
@@ -6,6 +6,7 @@
 
 #include "base/bind_helpers.h"
 #include "content/browser/download/download_item_impl.h"
+#include "content/browser/download/download_task_runner.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
 
@@ -48,8 +49,8 @@ WebContents* DownloadJob::GetWebContents() const {
 void DownloadJob::Start(DownloadFile* download_file_,
                         const DownloadFile::InitializeCallback& callback,
                         const DownloadItem::ReceivedSlices& received_slices) {
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
+  GetDownloadTaskRunner()->PostTask(
+      FROM_HERE,
       base::Bind(&DownloadFile::Initialize,
                  // Safe because we control download file lifetime.
                  base::Unretained(download_file_),
@@ -75,10 +76,10 @@ bool DownloadJob::AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
     return false;
 
   // download_file_ is owned by download_item_ on the UI thread and is always
-  // deleted on the FILE thread after download_file_ is nulled out.
+  // deleted on the download task runner after download_file_ is nulled out.
   // So it's safe to use base::Unretained here.
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
+  GetDownloadTaskRunner()->PostTask(
+      FROM_HERE,
       base::Bind(&DownloadFile::AddByteStream, base::Unretained(download_file),
                  base::Passed(&stream_reader), offset, length));
   return true;