[Skia Mac] Make misspelling underline dots unclipped

[Skia Mac] Make misspelling underline dots unclipped
https://bugs.webkit.org/show_bug.cgi?id=78117
http://code.google.com/p/chromium/issues/detail?id=113154

Reviewed by Stephen White.

No new tests. Existing layout tests cover this.

As is done on the CoreGraphics Mac platform, adjust the
underline width to remove partial dots, not including the
trailing transparent pixel column.

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

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107097 268f45cc-cd09-0410-ab3c-d52691b4dbfc