Make the page group use the proper link hashing functions rather than
calling the string hash functions directly. Add Chromium-specfic ifdefs
in the visited link computation functions to allow integration.

* page/PageGroup.cpp:
(WebCore::PageGroup::isLinkVisited):
(WebCore::PageGroup::addVisitedLink):
* platform/LinkHash.cpp:
(WebCore::visitedLinkHash):
* platform/LinkHash.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@39060 268f45cc-cd09-0410-ab3c-d52691b4dbfc