Unreviewed trivial prospective build fix for A17n disabled
configurations.

The dummy computed object attriute cache control functions need to be defined
as being member functions of AXObjectCache, because that's where they are
declared.

* accessibility/AXObjectCache.h:
(WebCore::AXObjectCache::startCachingComputedObjectAttributesUntilTreeMutates):
(WebCore::AXObjectCache::stopCachingComputedObjectAttributes):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141694 268f45cc-cd09-0410-ab3c-d52691b4dbfc