Roll src/third_party/skia 8c6c8b0..3838fe3 (3 commits) (#13105)

https://skia.googlesource.com/skia.git/+log/8c6c8b0c42e2..3838fe3c82b4

git log 8c6c8b0..3838fe3 --date=short --no-merges --format='%ad %ae %s'
2019-10-11 herb@google.com Use SkDrawableGlyphBuffer for bitmap rendering
2019-10-11 rsesek@chromium.org Switch SkSemaphore to use dispatch_semaphore_t on Mac.
2019-10-11 recipe-mega-autoroller@chops-service-accounts.iam.gserviceaccount.com Roll recipe dependencies (trivial).

Created with:
  gclient setdep -r src/third_party/skia@3838fe3c82b4

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 kjlubick@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=kjlubick@google.com

Author: skia-flutter-autoroll

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': '8c6c8b0c42e2e3d92d596bc950aedfecdd814d5d',
+  'skia_revision': '3838fe3c82b4c2bf5eb420a351a6f63ee668d8d7',
 
   # 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

@@ -1,4 +1,4 @@
-Signature: 7e1c50b87af7396c0f85b3bf776a0ea5
+Signature: cf6fcce8933676cb66739929493a01ce
 
 UNUSED LICENSES: