Continue making XSSAuditor thread safe: Remove unsafe AtomicString compares
https://bugs.webkit.org/show_bug.cgi?id=108557

Reviewed by Adam Barth.

Unfortunately HTMLNames comparisons will always be false on a non-main thread
with our current design, so we have to use some "threadSafeMatch" helpers written
for the HTMLBackgroundParser.

Also factor out threadSafeMatch() methods to HTMLParserIdioms.

No new tests because no new functionality.

* html/parser/BackgroundHTMLParser.cpp:
(WebCore):
* html/parser/HTMLParserIdioms.cpp:
(WebCore::threadSafeEqual):
(WebCore):
(WebCore::threadSafeMatch):
* html/parser/HTMLParserIdioms.h:
(WebCore):
* html/parser/XSSAuditor.cpp:
(WebCore::XSSAuditor::eraseAttributeIfInjected):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141686 268f45cc-cd09-0410-ab3c-d52691b4dbfc