Roll src/third_party/skia 31ff298:a9e8476

Summary of changes available at:
https://chromium.googlesource.com/skia/+log/31ff298..a9e8476

CQ_EXTRA_TRYBOTS=tryserver.blink:linux_blink_rel,linux_blink_dbg
TBR=borenet@google.com

Review URL: https://codereview.chromium.org/873023002

Cr-Commit-Position: refs/heads/master@{#313032}

DEPS

@@ -42,7 +42,7 @@ vars = {
   'boringssl_git': 'https://boringssl.googlesource.com',
   'libvpx_revision': 'cc9c0c5198e416173f480fb1f11e052f5c29a95b',
   'sfntly_revision': '1bdaae8fc788a5ac8936d68bf24f37d977a13dac',
-  'skia_revision': '31ff29829e3ceb8f5af0a655285d83abb6662c85',
+  'skia_revision': 'a9e84767e40bc0d4be8a03935a23b607cc4cb927',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.