Roll src/third_party/skia 37a88b4..21df075 (2 commits) (#14549)

https://skia.googlesource.com/skia.git/+log/37a88b43637e..21df075cab00

git log 37a88b4..21df075 --date=short --first-parent --format='%ad %ae %s'
2019-12-18 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 5407aaa..751e788 (13 commits)
2019-12-18 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader fbbfeb700295..21be09d8e699 (17 commits)

Created with:
  gclient setdep -r src/third_party/skia@21df075cab00

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 borenet@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: borenet@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': '37a88b43637e37d8cf706e25a2e2bb5c3fe38b09',
+  'skia_revision': '21df075cab00b771ffc495707bb59d14160df513',
 
   # 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: 8e1e3366b29c9aaec2b77968f5200c92
+Signature: 88e12fb1550820c171482e916cabcb67
 
 UNUSED LICENSES: