Remove GC code duplication in http/tests LayoutTests.
https://bugs.webkit.org/show_bug.cgi?id=111589

Reviewed by Kentaro Hara, Alexey Proskuryakov.

Replaced duplicated GC logic in various tests with a function call to the implementation
in /js-test-resources/js-test-pre.js

* http/tests/appcache/destroyed-frame.html:
* http/tests/media/media-source/video-media-source-sourcebufferlist-crash.html:
* http/tests/misc/async-script.html:
* http/tests/misc/embed-image-load-outlives-gc-without-crashing.html:
* http/tests/misc/image-input-type-outlives-gc-without-crashing.html:
* http/tests/misc/image-load-outlives-gc-without-crashing.html:
* http/tests/misc/javascript-url-stop-loaders.html:
* http/tests/misc/object-image-load-outlives-gc-without-crashing.html:
* http/tests/misc/svg-image-load-outlives-gc-without-crashing.html:
* http/tests/misc/video-poster-image-load-outlives-gc-without-crashing.html:
* http/tests/security/detached-sandboxed-frame-access.html:
* http/tests/websocket/tests/hybi/websocket-pending-activity.html:
* http/tests/xmlhttprequest/event-listener-gc.html:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145090 268f45cc-cd09-0410-ab3c-d52691b4dbfc