Fix use-after-free in geolocation layout test code introduced in r175404.

BUG=380588
TBR=ojan

Review URL: https://codereview.chromium.org/319503004

git-svn-id: svn://svn.chromium.org/blink/trunk@175510 bbb929c8-8fbe-4397-9dbb-9b2b20218538