Reviewed by Adele Peterson.

        Use a better technique to handle finding out if something responds to a selector
        in WebHTMLView's doCommandBySelector method.

        * WebView/WebHTMLView.mm:
        (-[WebHTMLView doCommandBySelector:]): Removed unneeded check for 0 coreFrame;
        this is already handled by coreCommandBySelector: so doesn't need to be checked
        twice. Got rid of initial value for eventWasHandled boolean to make it more clear.
        Use WebResponderChainSink to find out if a command is handled rather than walking
        the responder chain explicitly.
        (-[WebResponderChainSink initWithResponderChain:]): Added.
        (-[WebResponderChainSink detach]): Added.
        (-[WebResponderChainSink receivedUnhandledCommand]): Added.
        (-[WebResponderChainSink noResponderFor:]): Added.
        (-[WebResponderChainSink doCommandBySelector:]): Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@41859 268f45cc-cd09-0410-ab3c-d52691b4dbfc