Update GOM unittests to pass

Not sure why the tests changed from expecting '' to undefined,
but I doubt it matters.  Useful to be able to start from
all tests passing.

TBR=ojan@chromium.org
BUG=389681

Review URL: https://codereview.chromium.org/353183003

git-svn-id: svn://svn.chromium.org/blink/trunk@177134 bbb929c8-8fbe-4397-9dbb-9b2b20218538