Cache <font face> family lists in CSSValuePool.

Cache <font face> family lists in CSSValuePool.
<http://webkit.org/b/79195>

Reviewed by Antti Koivisto.

HTMLFontElements with "face" attributes are very common in legacy web content.
Add a String->CSSValue cache for these in CSSValuePool and use it to avoid
reparsing and recreating duplicate font face values.

This knocks 20ms (~1.5%) worth of samples off of the Moz page cycler on my system.

* css/CSSParser.cpp:
(WebCore::CSSParser::parseFontFaceValue):
* css/CSSParser.h:
* css/CSSValuePool.cpp:
(WebCore::CSSValuePool::createFontFaceValue):
* css/CSSValuePool.h:
* html/HTMLFontElement.cpp:
(WebCore::HTMLFontElement::collectStyleForAttribute):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108451 268f45cc-cd09-0410-ab3c-d52691b4dbfc