Conditionalize cross-document messaging support

 Conditionalize cross-document messaging support

 top level:

         Conditionalize cross-document messaging support

         The cross-document messaging parts of HTML 5 are in flux and we want
         ports to be able to turn off the support as needed.

         Note that the support is turned off by default right now. A subsequent
         commit will turn it on by default.

         Reviewed by Darin.

         * configure.ac:

 WebCore:

         Conditionalize cross-document messaging support

         The cross-document messaging parts of HTML 5 are in flux and we want
         ports to be able to turn off the support as needed.

         Note that the support is turned off by default right now. A subsequent
         commit will turn it on by default.

         Reviewed by Darin.

         * GNUmakefile.am:
         * WebCore.vcproj/build-generated-files.sh:
         * bindings/js/JSDOMWindowCustom.cpp:
         (WebCore::JSDOMWindow::customGetOwnPropertySlot):
         * bindings/js/JSEventCustom.cpp:
         (WebCore::toJS):
         * dom/Event.cpp:
         (WebCore::Event::isMessageEvent):
         * dom/Event.h:
         * dom/MessageEvent.cpp:
         * dom/MessageEvent.h:
         * dom/MessageEvent.idl:
         * page/DOMWindow.cpp:
         (WebCore::DOMWindow::postMessage):
         * page/DOMWindow.h:
         * page/DOMWindow.idl:

 WebKitTools:

         Conditionalize cross-document messaging support

         The cross-document messaging parts of HTML 5 are in flux and we want
         ports to be able to turn off the support as needed.

         Note that the support is turned off by default right now. A subsequent
         commit will turn it on by default.

         Reviewed by Darin.

         * Scripts/build-webkit:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@30269 268f45cc-cd09-0410-ab3c-d52691b4dbfc