Files.app: Fix a null exception of FileTransferController.

BUG=None
TEST=manually
R=mtomasz@chromium.org

Review URL: https://codereview.chromium.org/244693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@264966 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed