Roll Dart SDK from 4693d6d4f88e to b77641194368 (3 revisions) (#24836)

https://dart.googlesource.com/external/github.com/flutter/engine/+/ce21b840bac94c88ccc92890ac9a1b3b5318710b
diff --git a/commits.json b/commits.json
index 3af8ddb..2249365 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"c49b2fa6cfb04c5ca0fedc70751082a5c13b7b50",
+  "external/github.com/flutter/engine":"ce21b840bac94c88ccc92890ac9a1b3b5318710b",
   "external/github.com/flutter/flutter":"a0ba6464089f906fefbf610732b2c9a7b66a1260",
   "sdk":"b683098fde9611cea472cb081da2cea7ba15bc8b"
 }
\ No newline at end of file