Roll src/third_party/skia ab52a7a53db6..57ef68077574 (3 commits) (#12396)

https://skia.googlesource.com/skia.git/+log/ab52a7a53db6..57ef68077574

git log ab52a7a53db6..57ef68077574 --date=short --no-merges --format='%ad %ae %s'
2019-09-23 robertphillips@google.com Create a GrGpu::createBackendTexture choke point
2019-09-23 bsalomon@google.com Remove a few GrSurfaceProxy::config() usages
2019-09-23 brianosman@google.com Roll third_party/externals/angle2 6c4ff5ddab07..8be7a4c7f738 (12 commits)

Created with:
  gclient setdep -r src/third_party/skia@57ef68077574

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 bungeman@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=bungeman@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': 'ab52a7a53db6ab1060d366d989f1b797f2b2f598',
+  'skia_revision': '57ef6807757454891a57cdc42a32f26f40a8b2bf',
 
   # 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: bb75bc3812bd490831a12ffccde8b758
+Signature: bbfc49d6c1f618ea0fcbc684ad260e7c
 
 UNUSED LICENSES: