Roll src/third_party/skia/ 901257a3b..6af0c958a (2 commits).

https://chromium.googlesource.com/skia.git/+log/901257a3ba1d..6af0c958a0d0

$ git log 901257a3b..6af0c958a --date=short --no-merges --format='%ad %ae %s'
2016-07-22 mtklein GN: restore gn.py partly as fetch-gn
2016-07-22 caryclark conic fuzz fix

BUG=630378

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_blink_rel
TBR=jcgregorio@google.com

Review-Url: https://codereview.chromium.org/2175693002
Cr-Commit-Position: refs/heads/master@{#407131}

DEPS

@@ -36,7 +36,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and whatever else without interference from each other.
-  'skia_revision': '901257a3ba1d094280b4e1e0868bc0bcd137145a',
+  'skia_revision': '6af0c958a0d024f65a9049f5b84793e03b781801',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.