Don't clear IntentRequest callback pointers on stop()

Don't clear IntentRequest callback pointers on stop()

This causes re-entry into ScriptExecutionContext when
the ActiveDOMCallback objects get deleted, which crashes.
Instead, just de-activate the object and wait for
context destruction to clean up.

Test crashes consistently without fix and passes with fix.
Added some test infrastructure to support this test.
https://bugs.webkit.org/show_bug.cgi?id=78638

Patch by Greg Billock <gbillock@google.com> on 2012-02-23
Reviewed by Adam Barth.

* Modules/intents/IntentRequest.cpp:
(WebCore::IntentRequest::IntentRequest):
(WebCore::IntentRequest::stop):
(WebCore::IntentRequest::postResult):
(WebCore::IntentRequest::postFailure):
* Modules/intents/IntentRequest.h:
(IntentRequest):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108724 268f45cc-cd09-0410-ab3c-d52691b4dbfc