Coverity: fix leak when AutomationProvider::WaitForDownloadsToComplete called with zero downloads.
Coverity: fix leak when AutomationProvider::WaitForDownloadsToComplete called with zero downloads.

CID=9160
TEST=trybots
BUG=none

Review URL: http://codereview.chromium.org/2934002

git-svn-id: http://src.chromium.org/svn/trunk/src@52030 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 017faca18a9e234429f8d4cd49856b21d53b4487
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser