Reviewed by Darin Adler.

        Move coordinate-computing logic into MouseRelatedEvent.
        https://bugs.webkit.org/show_bug.cgi?id=57521

        Refactoring, covered by existing tests.

        * dom/EventDispatcher.cpp:
        (WebCore::EventDispatcher::dispatchWheelEvent): Yank calculation of
            coordinates out.
        (WebCore::EventDispatcher::dispatchMouseEvent): Ditto.
        * dom/MouseEvent.cpp:
        (WebCore::MouseEvent::create): Add coordinate-computing logic.
        * dom/MouseEvent.h: Adjust decl to reflect new meaning of params.
        * dom/MouseRelatedEvent.cpp:
        (WebCore::MouseRelatedEvent::MouseRelatedEvent): Ditto.
        * page/EventHandler.cpp:
        (WebCore::EventHandler::dispatchDragEvent): Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@82584 268f45cc-cd09-0410-ab3c-d52691b4dbfc