GitLab

ChromeThread::IO will be used to cancel URLFetcher request and
clean up URLRequestContextGetter.

BUG=52562,52826
TEST=valgrind passes

Review URL: http://codereview.chromium.org/3176028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@57032 0039d316-1c4b-4281-b951-d872f2087c98