Roll Dart SDK from 966078df3a25 to 89fe12b12aab (2 revisions) (#19766)

diff --git a/DEPS b/DEPS
index 181bb05..f54718f 100644
--- a/DEPS
+++ b/DEPS
@@ -34,7 +34,7 @@
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '966078df3a2514a0ce24c61dd674e1c5a9df6fba',
+  'dart_revision': '89fe12b12aab50d0db1f9e30190afb32c754a900',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py