https://bugs.webkit.org/show_bug.cgi?id=34150
        WebKit needs a mechanism to catch stale HashMap entries

        It is very difficult to catch stale pointers that are HashMap keys - since a pointer's hash
        is just its value, it is very unlikely that any observable problem is reproducible.

        This extends hash table consistency checks to check that pointers are referencing allocated
        memory blocks, and makes it possible to invoke the checks explicitly (it is not feasible
        to enable CHECK_HASHTABLE_CONSISTENCY by default, because that affects performance too much).

        * wtf/HashMap.h: (WTF::::checkConsistency): Call through to HashTable implementation. We can
        add similar calls to HashSet and HashCountedSet, but I haven't seen hard to debug problems
        with those yet.

        * wtf/HashSet.h: (WTF::::remove): The version of checkTableConsistency that's guarded by
        CHECK_HASHTABLE_CONSISTENCY is now called internalCheckTableConsistency().

        * wtf/HashTable.h:
        (WTF::HashTable::internalCheckTableConsistency):
        (WTF::HashTable::internalCheckTableConsistencyExceptSize):
        (WTF::HashTable::checkTableConsistencyExceptSize):
        Expose checkTableConsistency() even if CHECK_HASHTABLE_CONSISTENCY is off.
        (WTF::::add): Updated for checkTableConsistency renaming.
        (WTF::::addPassingHashCode): Ditto.
        (WTF::::removeAndInvalidate): Ditto.
        (WTF::::remove): Ditto.
        (WTF::::rehash): Ditto.
        (WTF::::checkTableConsistency): The assertion for !shouldExpand() was not correct - this
        function returns true for tables with m_table == 0.
        (WTF::::checkTableConsistencyExceptSize): Call checkValueConsistency for key. Potentially,
        we could do the same for values.

        * wtf/HashTraits.h:
        (WTF::GenericHashTraits::checkValueConsistency): An empty function that can be overridden
        to add checks. Currently, the only override is for pointer hashes.

        * wtf/RefPtrHashMap.h: (WTF::::remove): Updated for checkTableConsistency renaming.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@53899 268f45cc-cd09-0410-ab3c-d52691b4dbfc