Shortened URLRequestContextGetter's lifetime, which was extended by DownloadManager.

BUG=58726
TEST=None

Review URL: http://codereview.chromium.org/3697007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@65417 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/download/download_manager.cc b/chrome/browser/download/download_manager.cc
index 106c8fc..7669d9e 100644
--- a/chrome/browser/download/download_manager.cc
+++ b/chrome/browser/download/download_manager.cc
@@ -136,6 +136,8 @@
 
   download_history_.reset();
 
+  request_context_getter_ = NULL;
+
   shutdown_needed_ = false;
 }