Fix crash in ResourceLoader::requestSychronously.

This was caused by http://src.chromium.org/viewvc/blink/?revision=159159&view=revision

BUG=306346
TEST=The cluster fuzz repro doesn't seem to crash in content_shell :(

Review URL: https://codereview.chromium.org/27195005

git-svn-id: svn://svn.chromium.org/blink/trunk@159863 bbb929c8-8fbe-4397-9dbb-9b2b20218538