Slider cleanup.  Let the theme set the size of the slider thumb.

        * rendering/RenderSlider.cpp:
        (WebCore::RenderSlider::setStyle): Moving the thumb's appearance adjustment to createThumbStyle.
        (WebCore::RenderSlider::createThumbStyle):
        (WebCore::RenderSlider::layout): Let the theme set the size of the thumb.
        * rendering/RenderTheme.cpp: (WebCore::RenderTheme::adjustSliderThumbSize):  Added.
        * rendering/RenderTheme.h: ditto.
        * rendering/RenderThemeMac.h: ditto.
        * rendering/RenderThemeMac.mm: (WebCore::RenderThemeMac::adjustSliderThumbSize): ditto.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@17823 268f45cc-cd09-0410-ab3c-d52691b4dbfc