Reviewed by Andreas Kling.

        [Qt] JSC Bridge: convert QtConnectionObject to use JSC API
        https://bugs.webkit.org/show_bug.cgi?id=62330

        This patch is based on the draft patch by Noam Rosenthal in bug 60842.
        Qt API autotests cover the bridge behavior and pass after this patch.

        * bridge/qt/qt_runtime.h: Change QtConnectionObject to use JSC API types. In
        particular, we got rid of Strong<JSObject> members. Renamed some members and
        arguments to follow existing naming in QObject::connect().

        * bridge/qt/qt_runtime.cpp:
        (JSC::Bindings::QtRuntimeConnectionMethod::call): Use a new helper function
        to create a connection, passing the ExecState* that will be used when the
        connection is activated (signal emitted). Use JSC API types when looking up
        the matching signal to disconnect.

        (JSC::Bindings::QtConnectionObject::QtConnectionObject): Use JSC API to
        protect the receiver and receiverFunction from being garbage
        collected. Removed the ASSERT() since we don't hold ProtectedPtrs (in current
        code were Strong<>) anymore.

        (JSC::Bindings::QtConnectionObject::~QtConnectionObject): Explain why is safe
        to use m_originalSender here. Unprotect values that we protected in constructor.

        (JSC::Bindings::isJavaScriptFunction): Helper function to identify whether a
        JSObjectRef is a JS function (in contrast to a native function exposed to JS).

        (JSC::Bindings::QtConnectionObject::execute):
        (JSC::Bindings::QtConnectionObject::match):
        Both updated to use JSC API when appliable. Note that convertQVariantToValue
        still returns JSC internal types, will be handled in a different patch.

        (JSC::Bindings::QtConnectionObject::createWithInternalJSC):
        Convenince for the existing caller until it is converted to JSC as well.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@88635 268f45cc-cd09-0410-ab3c-d52691b4dbfc