Roll src/third_party/skia dd0dff1c35d2..8391bac5c6f0 (8 commits) (#12337)

https://skia.googlesource.com/skia.git/+log/dd0dff1c35d2..8391bac5c6f0

git log dd0dff1c35d2..8391bac5c6f0 --date=short --no-merges --format='%ad %ae %s'
2019-09-18 bsalomon@google.com Add F16Norm mode to viewer
2019-09-18 bsalomon@google.com blurrect_compare GM: draw "masks" in white for RGBA fallback.
2019-09-18 csmartdalton@google.com Weed out duplicates from the proxy version of addDependency
2019-09-18 mtklein@google.com faster PNG encoding in skottie_tool
2019-09-18 csmartdalton@google.com Revert "Use a "decal" domain for filterMaskGPU"
2019-09-18 csmartdalton@google.com Revert "Abolish absClear"
2019-09-18 bsalomon@google.com Use mipmapping/protected to lookup scratch textures.
2019-09-18 jvanverth@google.com Reland "Add ETC2 support to Metal backend."

Created with:
  gclient setdep -r src/third_party/skia@8391bac5c6f0

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC brianosman@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

Bug: None
TBR=brianosman@google.com

DEPS

@@ -26,7 +26,7 @@ vars = {
   'skia_git': 'https://skia.googlesource.com',
   # OCMock is for testing only so there is no google clone
   'ocmock_git': 'https://github.com/erikdoe/ocmock.git',
-  'skia_revision': 'dd0dff1c35d2944ca6fb542bcec7ebae88ca1680',
+  'skia_revision': '8391bac5c6f07fd01e78cc140b01119de73a749d',
 
   # 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: eb7ed06cb0163e6506026d6a9c4c08c9
+Signature: 1b5f47ed20d6f30d22cffd59efe3d10b
 
 UNUSED LICENSES: