Roll Skia from 462bdece17bf to 684f3a831216 (3 revisions) (flutter#175641)

https://skia.googlesource.com/skia.git/+log/462bdece17bf..684f3a831216

2025-09-19 skia-autoroll@skia-public.iam.gserviceaccount.com Roll
SwiftShader from ce5b85176a89 to 7dd631d218ad (1 revision)
2025-09-19 skia-autoroll@skia-public.iam.gserviceaccount.com Roll Skia
Infra from 3d311dfa7fdd to d549c8c3724a (7 revisions)
2025-09-19 skia-autoroll@skia-public.iam.gserviceaccount.com Roll Dawn
from d88a7a749566 to 67b75214b0b5 (6 revisions)

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
chinmaygarde@google.com,kjlubick@google.com,michaelludwig@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://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Author: engine-flutter-autoroll

DEPS

@@ -14,7 +14,7 @@ vars = {
   'flutter_git': 'https://flutter.googlesource.com',
   'skia_git': 'https://skia.googlesource.com',
   'llvm_git': 'https://llvm.googlesource.com',
-  'skia_revision': '462bdece17bf81cd45ef47881950933f79228bfa',
+  'skia_revision': '684f3a8312165aa036146441d77f0575919b0b89',
 
   # WARNING: DO NOT EDIT canvaskit_cipd_instance MANUALLY
   # See `lib/web_ui/README.md` for how to roll CanvasKit to a new version.