IndexedDB: Re-enable a pair of bindings tests

Apparently these were disabled back in http://wkrev.com/r140449 (~6
months ago) as a result of flakiness after http://wkrev.com/140392 and
no-one followed up. Oops.

Seem fine locally, so assuming it was something during Isolate-a-palooza
that has since been sorted out. Fingers crossed...

R=haraken@chromium.org,abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/19772012

git-svn-id: svn://svn.chromium.org/blink/trunk@155130 bbb929c8-8fbe-4397-9dbb-9b2b20218538