Pass script state to Web API object->script wrappable converter.

This is required to create script wrappable objects which depend on
their execution context, such as EventTargets and ActiveDOMObjects.

BUG=349919
TBR=mvanouwerkerk@chromium.org

Review URL: https://codereview.chromium.org/236133002

git-svn-id: svn://svn.chromium.org/blink/trunk@171413 bbb929c8-8fbe-4397-9dbb-9b2b20218538