Fix for http://bugzilla.opendarwin.org/show_bug.cgi?id=6755 CSS3: 
        Borders rounded with border-radius don't draw the roundings

        This patch does not draw all of the different border styles 
        perfectly, so I have filed a few followup bugs that I will 
        reference from this Bugzilla.

        * platform/GraphicsContext.h:
        * platform/cairo/GraphicsContextCairo.cpp:
        (WebCore::GraphicsContext::drawArc): drawArc() has different 
        parameters now, but mostly this needs to be implemented to match 
        the Mac side later.
        (WebCore::GraphicsContext::addRoundedRectClip): Just a stub. 
        Implement this later.
        (WebCore::GraphicsContext::addInnerRoundedRectClip): Just a stub. 
        Implement this later.
        * platform/cg/GraphicsContextCG.cpp:
        (WebCore::GraphicsContext::drawArc): drawArc() now handles drawing 
        elliptical arcs as well as circular arcs, it also takes a thickness 
        parameter to draw an arc of a given thickness and draws with the 
        appropriate pen style.
        (WebCore::GraphicsContext::addInnerRoundedRectClip): Adds a clip to 
        the inside of an arc instead of to the outside which is already 
        done by addRoundedClipRect()
        * rendering/RenderObject.cpp:
        (WebCore::RenderObject::drawBorderArc): Draws the border arcs in 
        the appropriate styles.
        (WebCore::RenderObject::paintBorder): Calls drawBorderArc() when 
        border arcs are needed.
        * rendering/RenderObject.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@14650 268f45cc-cd09-0410-ab3c-d52691b4dbfc