Reviewed by Eric Seidel.

        [Haiku] Adding modification to the WebCore/platform/ files to allow
        the Haiku port.
        https://bugs.webkit.org/show_bug.cgi?id=28128

        * platform/ContextMenuItem.h: BMenu is the PlatformMenuItemDescription
        class of Haiku.
        * platform/Cursor.h: BCursor is the Cursor class of Haiku.
        * platform/DragData.h: Use a BMessage as DragDataRef.
        * platform/DragImage.h: Use a BBitmap as DragImageRef.
        * platform/PlatformKeyboardEvent.h: Use BMessage as event vehicle.
        * platform/PlatformMenuDescription.h: BMenu is the
        PlatformMenuDescription class of Haiku.
        * platform/PlatformMouseEvent.h: Use BMessage as event vehicle.
        * platform/PlatformWheelEvent.h: Use BMessage as event vehicle.
        * platform/PopupMenu.h: Adding a m_menu attribute for Haiku.
        * platform/Widget.h: BView is the PlatformWidget class of Haiku.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@47145 268f45cc-cd09-0410-ab3c-d52691b4dbfc