Roll Dart SDK from 3367c66051ce to 4b5af9312298 (2 revisions) (#20719)

diff --git a/DEPS b/DEPS
index b2140bb..50b5cdf 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': '3367c66051ce0b17c9d895ae3600f0c107d7a0cf',
+  'dart_revision': '4b5af931229871e289627530499cf6303e393032',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py