Roll src/third_party/skia/ 64b70b096..a8b1e6d06 (1 commit).

https://skia.googlesource.com/skia.git/+log/64b70b096ac2..a8b1e6d0688c

$ git log 64b70b096..a8b1e6d06 --date=short --no-merges --format='%ad %ae %s'
2016-12-19 rmistry Revert of Generate Signed Distance Field directly from vector path (patchset #23 id:440001 of https://codereview.chromium.org/1643143002/ )

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
TBR=rmistry@google.com

Review-Url: https://codereview.chromium.org/2586983002
Cr-Commit-Position: refs/heads/master@{#439464}

DEPS

@@ -40,7 +40,7 @@ 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': '64b70b096ac20833d9737758a4bd5f2a51078bc4',
+  'skia_revision': 'a8b1e6d0688c7bc8754b0f49578144c77f5a180e',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.