Downloads: replace BrowserThread::FILE with task scheduler.

chrome/browser/download/download_browsertest.cc

Index: chrome/browser/download/download_browsertest.cc
diff --git a/chrome/browser/download/download_browsertest.cc b/chrome/browser/download/download_browsertest.cc
index 73ad71faf517d679c94d1b9780b007e079a30073..b7b014a5814b1f16b1705cf784b808f1c5a9c5fb 100644
--- a/chrome/browser/download/download_browsertest.cc
+++ b/chrome/browser/download/download_browsertest.cc
@@ -916,8 +916,7 @@ class DownloadTest : public InProcessBrowserTest {
     }
 
     // Wait till the |DownloadFile|s are destroyed.
-    content::RunAllPendingInMessageLoop(content::BrowserThread::FILE);
-    content::RunAllPendingInMessageLoop(content::BrowserThread::UI);
+    content::RunAllBlockingPoolTasksUntilIdle();
 
     // Validate that the correct files were downloaded.
     download_items.clear();