Roll src/third_party/skia 8c6c8b0c42e2..3838fe3c82b4 (3 commits)

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

git log 8c6c8b0c42e2..3838fe3c82b4 --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-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

CQ_INCLUDE_TRYBOTS=luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux-blink-rel;luci.chromium.try:linux-chromeos-compile-dbg;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
TBR=kjlubick@google.com

Bug: chromium:1012386
Change-Id: I32f23917d4326375c505e852e762d755f45914e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1857559Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#705328}

DEPS

@@ -167,7 +167,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and whatever else without interference from each other.
-  'skia_revision': '8c6c8b0c42e2e3d92d596bc950aedfecdd814d5d',
+  'skia_revision': '3838fe3c82b4c2bf5eb420a351a6f63ee668d8d7',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.