Reviewed by Maciej.

        - https://bugs.webkit.org/show_bug.cgi?id=19434
          speed up SunSpider by avoiding some string boxing

        Speeds up SunSpider by 1.1%.

        Optimized code path for getting built-in properties from strings -- avoid
        boxing with a string object in that case. We can make further changes to avoid
        even more boxing, but this change alone is a win.

        * API/JSCallbackObjectFunctions.h:
        (KJS::JSCallbackObject::staticValueGetter): Use isObject instead of inherits
        in asssert, since the type of slotBase() is now JSValue, not JSObject.
        (KJS::JSCallbackObject::staticFunctionGetter): Ditto.
        (KJS::JSCallbackObject::callbackGetter): Ditto.

        * kjs/internal.cpp:
        (KJS::StringImp::getPrimitiveNumber): Updated for change of data member name.
        (KJS::StringImp::toBoolean): Ditto.
        (KJS::StringImp::toNumber): Ditto.
        (KJS::StringImp::toString): Ditto.
        (KJS::StringInstance::create): Added; avoids a bit of cut and paste code.
        (KJS::StringImp::toObject): Use StringInstance::create.
        (KJS::StringImp::toThisObject): Ditto.
        (KJS::StringImp::lengthGetter): Added. Replaces the getter that used to live in
        the StringInstance class.
        (KJS::StringImp::indexGetter): Ditto.
        (KJS::StringImp::indexNumericPropertyGetter): Ditto.
        (KJS::StringImp::getOwnPropertySlot): Added. Deals with built in properties of
        the string class without creating a StringInstance.

        * kjs/internal.h:
        (KJS::StringImp::getStringPropertySlot): Added. To be used by both the string
        and string object getOwnPropertySlot function.

        * kjs/lookup.h:
        (KJS::staticFunctionGetter): Updated since slotBase() is now a JSValue rather
        than a JSObject.

        * kjs/object.h: Removed PropertySlot::slotBase() function, which can now move
        back into property_slot.h where it belongs since it doesn't have to cast to
        JSObject*.

        * kjs/property_slot.cpp:
        (KJS::PropertySlot::functionGetter): Updated since slot.slotBase() is now a JSValue*
        instead of JSObject*. setGetterSlot still guarantees the base is a JSObject*.
        * kjs/property_slot.h:
        (KJS::PropertySlot::PropertySlot): Changed base to JSValue* intead of JSCell*.
        (KJS::PropertySlot::setStaticEntry): Ditto.
        (KJS::PropertySlot::setCustom): Ditto.
        (KJS::PropertySlot::setCustomIndex): Ditto.
        (KJS::PropertySlot::setCustomNumeric): Ditto.
        (KJS::PropertySlot::slotBase): Moved inline here since it no longer involves a
        downcast to JSObject*.
        (KJS::PropertySlot::setBase): Changed to JSValue*.

        * kjs/string_object.cpp:
        (KJS::StringInstance::getOwnPropertySlot): Changed to use getStringPropertySlot
        instead of coding the properties here. This allows sharing the code with StringImp.

        * kjs/string_object.h: Removed inlineGetOwnPropertySlot, lengthGetter, and indexGetter.
        Made one of the constructors protected.

        * kjs/value.h: Made getOwnPropertySlot private in the JSCell class -- this is better
        since it's not the real JSObject getOwnPropertySlot semantic and most callers shouldn't
        use it.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@34518 268f45cc-cd09-0410-ab3c-d52691b4dbfc