Roll Skia from a2728a7ad2a3 to 6f4fd97d2f7e (2 revisions) (flutter/engine#45278)

https://skia.googlesource.com/skia.git/+log/a2728a7ad2a3..6f4fd97d2f7e

2023-08-30 kjlubick@google.com Add external_client workspace for testing consuming Skia rules
2023-08-30 lovisolo@google.com [bazel] //gm/BazelGMRunner.cpp: Improve structure of output JSON files.

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 aaclarke@google.com,brianosman@google.com,jlavrova@google.com,rmistry@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Skia: https://bugs.chromium.org/p/skia/issues/entry
To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose

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/+doc/main/autoroll/README.md

DEPS

@@ -18,7 +18,7 @@ vars = {
   'llvm_git': 'https://llvm.googlesource.com',
   # OCMock is for testing only so there is no google clone
   'ocmock_git': 'https://github.com/erikdoe/ocmock.git',
-  'skia_revision': 'a2728a7ad2a3471505475eedb485d46beb4b2e09',
+  'skia_revision': '6f4fd97d2f7ef837b678787c2760854ebb838ee1',
 
   # WARNING: DO NOT EDIT canvaskit_cipd_instance MANUALLY
   # See `lib/web_ui/README.md` for how to roll CanvasKit to a new version.

engine/src/flutter/ci/licenses_golden/licenses_skia

@@ -1,4 +1,4 @@
-Signature: 3359875f162834261ec63e1bc66f60af
+Signature: 8a105ee3d77509b83d37b3f78c0f67ec
 
 ====================================================================================================
 LIBRARY: etc1