Reviewed by Justin Garcia.

        https://bugs.webkit.org/show_bug.cgi?id=16135
        [GTK] Support caret browsing

        Based on a patch by Alp Toker.

        Implement basic support for caret browsing, active only when the
        corresponding setting is enabled.

        * page/EventHandler.cpp:
        (WebCore::EventHandler::handleMouseReleaseEvent):
        * page/FocusController.cpp:
        (WebCore::FocusController::advanceFocus):
        (WebCore::clearSelectionIfNeeded):
        (WebCore::FocusController::setFocusedNode):
        * page/Frame.cpp:
        (WebCore::Frame::setFocusedNodeIfNeeded):
        (WebCore::Frame::setSelectionFromNone):
        (WebCore::Frame::respondToChangedSelection):
        * page/Settings.cpp:
        (WebCore::Settings::Settings):
        * page/Settings.h:
        * rendering/RenderBlock.cpp:
        (WebCore::RenderBlock::paintCaret):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@42924 268f45cc-cd09-0410-ab3c-d52691b4dbfc