Try to make some xssAuditor tests less flakey.

Try to make some xssAuditor tests less flakey.
https://bugs.webkit.org/show_bug.cgi?id=44749

Reviewed by Simon Fraser.

Use postMessage() to communicate to the top window each time a
beforeload event fires in the iframe. When the top window has seen a
beforeload event from each widget in the iframe, it calls notifyDone().
This prevents the test from exiting before all the widgets have had a
chance to load, therefore ensuring that all relevant XSS Auditor
messages have been emitted.

* http/tests/security/xssAuditor/object-embed-tag-control-char-expected.txt:
* http/tests/security/xssAuditor/object-embed-tag-control-char.html:
* http/tests/security/xssAuditor/object-embed-tag-expected.txt:
* http/tests/security/xssAuditor/object-embed-tag-null-char-expected.txt:
* http/tests/security/xssAuditor/object-embed-tag-null-char.html:
* http/tests/security/xssAuditor/object-embed-tag.html:
* http/tests/security/xssAuditor/object-src-inject.html:
* http/tests/security/xssAuditor/object-tag-javascript-url.html:
* http/tests/security/xssAuditor/object-tag.html:
* http/tests/security/xssAuditor/resources/echo-intertag.pl:
* http/tests/security/xssAuditor/resources/echo-object-src.pl:
* http/tests/security/xssAuditor/resources/utilities.js:
(notifyDoneAfterReceivingBeforeloadFromIds):
* platform/mac/Skipped:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@66254 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Conflicts:

	LayoutTests/platform/mac/Skipped