Add Skia build flags to WebKit skia gyp

Unreviewed change to enable easy layout test rebaselining.

* skia_webkit.gyp: Added SK_IGNORE_QUAD_STROKE_FIX and SK_IGNORE_TREAT_AS_SPRITE


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138949 268f45cc-cd09-0410-ab3c-d52691b4dbfc