Roll src/third_party/skia 6a8c3f07e81a..f4c66ccafcb7 (2 commits) (#9013)

https://skia.googlesource.com/skia.git
/%2Blog/6a8c3f07e81a..f4c66ccafcb7

git log 6a8c3f07e81a6647c7de1b6d9b7835435dbfe691..f4c66ccafcb7fe62201cbe9a6eb72b09ef8a31da --date=short --no-merges --format=%ad %ae %s
2019-05-20 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 06de90c66c18..70958d15db70 (8 commits)
2019-05-20 skia-autoroll@skia-public.iam.gserviceaccount.com Roll ../src 5ca9f9560554..4dc9df3b70d6 (533 commits)

The AutoRoll server is located here: https://autoroll.skia.org/r/skia-flutter-autoroll

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

If the roll is causing failures, please contact the current sheriff (csmartdalton@google.com), and stop
the roller if necessary.

DEPS

@@ -23,7 +23,7 @@ vars = {
   'fuchsia_git': 'https://fuchsia.googlesource.com',
   'github_git': 'https://github.com',
   'skia_git': 'https://skia.googlesource.com',
-  'skia_revision': '6a8c3f07e81a6647c7de1b6d9b7835435dbfe691',
+  'skia_revision': 'f4c66ccafcb7fe62201cbe9a6eb72b09ef8a31da',
 
   # When updating the Dart revision, ensure that all entries that are
   # dependencies of Dart are also updated to match the entries in the

ci/licenses_golden/licenses_skia

-Signature: 28dc54d9addeccc8e836c10251967656
+Signature: c9641b16573a65d0dc1a5602bda8f488
 
 UNUSED LICENSES: