Inset focus ring (Skia on Mac)

Inset focus ring (Skia on Mac)
https://bugs.webkit.org/show_bug.cgi?id=69166
http://code.google.com/p/chromium/issues/detail?id=97956

This focus ring was drawn too large and was left tracks
in subsequent invalidations. Make it more closely match
the CG version.

Reviewed by Stephen White.

No new tests. This platform is not enabled.

* platform/graphics/skia/GraphicsContextSkia.cpp:
(WebCore::getFocusRingOutset):
(WebCore::GraphicsContext::drawFocusRing):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@96426 268f45cc-cd09-0410-ab3c-d52691b4dbfc