[Chromium] IndexedDB/Worker crash during shutdown
https://bugs.webkit.org/show_bug.cgi?id=109467

Reviewed by Tony Chang.

If the message queue has already been terminated, don't bother scheduling
a new error event that will never be delivered. Speculative fix for the
issue, which only repros in multiprocess ports and so far only on some
platforms.

* src/IDBFactoryBackendProxy.cpp:
(WebKit::IDBFactoryBackendProxy::allowIndexedDB): Early exit.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142653 268f45cc-cd09-0410-ab3c-d52691b4dbfc