Reviewed by Andreas Kling.

        [WK2] Make non-transparent windowless plugins paint on X11
        https://bugs.webkit.org/show_bug.cgi?id=55660

        Implement painting for non-transparent windowless X11 plugins.
        The essence of the logic has been adapted from WebCore.
        The implementation is stubbed for GTK and working only on Qt
        but it should be really easy to finish it for GTK.

        * WebKit2.pro:
        * WebProcess/Plugins/Netscape/NetscapeBrowserFuncs.cpp:
        (WebKit::NPN_GetValue): Handle X11 specific values that are necessary.
        * WebProcess/Plugins/Netscape/NetscapePlugin.cpp:
        (WebKit::NetscapePlugin::NetscapePlugin): Initialize the X11 specific
        members that has been added.
        (WebKit::NetscapePlugin::callSetWindow): Always set the x and y coordinates
        of the NP_Window to 0 on X11 since we are using a backings store as the
        painting area for the plugin.
        * WebProcess/Plugins/Netscape/NetscapePlugin.h:
        * WebProcess/Plugins/Netscape/gtk/NetscapePluginGtk.cpp: Removed in favour
        of a common implementation for X11.
        * WebProcess/Plugins/Netscape/qt/NetscapePluginQt.cpp: Ditto.
        * WebProcess/Plugins/Netscape/x11/NetscapePluginX11.cpp: Added.
        (WebKit::getPluginDisplay):

        Platform specific static getters.
        (WebKit::x11Display):
        (WebKit::displayDepth):
        (WebKit::rootWindowID):
        (WebKit::x11Screen):

        (WebKit::NetscapePlugin::platformPostInitialize): Set up the visual
        settings and the colormap for the plugin.
        (WebKit::NetscapePlugin::platformDestroy):
        (WebKit::NetscapePlugin::platformInvalidate): Remained stub.
        (WebKit::NetscapePlugin::platformGeometryDidChange): Create a new
        pixmap that fits the geometry.
        (WebKit::NetscapePlugin::platformPaint): Propagate a paint event
        to the plugin, sync with it if necessary and draw the pixmap to
        the screen.
        (WebKit::toNP): Remained stub.
        (WebKit::NetscapePlugin::platformHandleMouseEvent): Remained stub.
        (WebKit::NetscapePlugin::platformHandleWheelEvent): Remained stub.
        (WebKit::NetscapePlugin::platformSetFocus): Remained stub.
        (WebKit::NetscapePlugin::platformHandleMouseEnterEvent): Remained stub.
        (WebKit::NetscapePlugin::platformHandleMouseLeaveEvent): Remained stub.
        (WebKit::NetscapePlugin::platformHandleKeyboardEvent): Remained stub.
        * WebProcess/WebCoreSupport/WebFrameLoaderClient.cpp:
        (WebKit::WebFrameLoaderClient::createPlugin): Hack. Inject wmode=opaque
        key-value pair to the plugin parameters to force Flash to act in
        non-transparent windowless mode. Qt also doing this in WebCore.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@80714 268f45cc-cd09-0410-ab3c-d52691b4dbfc