Roll src/third_party/skia/ 9081ceb12..830c91362 (2 commits).

https://chromium.googlesource.com/skia.git/+log/9081ceb1236d..830c913625ac

$ git log 9081ceb12..830c91362 --date=short --no-merges --format='%ad %ae %s'
2016-07-29 mtklein GN: ccache+clang needs -Qunused-arguments
2016-07-29 mtklein GN: Always quote cc and cxx.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
TBR=tomhudson@google.com

Review-Url: https://codereview.chromium.org/2195553003
Cr-Commit-Position: refs/heads/master@{#408634}

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': '9081ceb1236dfd1f3c7e9d5ef1d6f7c409d06aa1',
+  'skia_revision': '830c913625ac62b16b09cc0f1dbd8f177ec493d9',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.