Roll src/third_party/skia 938dfba:4e8955b

Summary of changes available at:
https://chromium.googlesource.com/skia/+log/938dfba..4e8955b

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

Review URL: https://codereview.chromium.org/632953002

Cr-Commit-Position: refs/heads/master@{#298391}

DEPS

@@ -44,7 +44,7 @@ vars = {
   'boringssl_git': 'https://boringssl.googlesource.com',
   'libvpx_revision': 'efe9712d52c2d216fb3d1ceb508b8148847a7e4b',
   'sfntly_revision': '1bdaae8fc788a5ac8936d68bf24f37d977a13dac',
-  'skia_revision': '938dfba51d0be03fa81866d99214447dac359e83',
+  'skia_revision': '4e8955b7720a9585b25313d57d140da5ac264d4c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.