[ServiceWorker] Throws InvalidStateError when calling postMessage on a redundant ServiceWorker.

BUG=410722
TEST=LayoutTests/http/tests/serviceworker/postmessage.html

Review URL: https://codereview.chromium.org/578573002

git-svn-id: svn://svn.chromium.org/blink/trunk@182044 bbb929c8-8fbe-4397-9dbb-9b2b20218538