Oilpan: fix build after r177450.

Update ScriptPromise tests to be Oilpan compatible.

R=haraken@chromium.org
BUG=363967
NOTRY=true

Review URL: https://codereview.chromium.org/367263004

git-svn-id: svn://svn.chromium.org/blink/trunk@177463 bbb929c8-8fbe-4397-9dbb-9b2b20218538