Fix unchecked operation warnings in FlutterMain (#9073)

Also remove trailing whitespace on some lines
https://dart.googlesource.com/external/github.com/flutter/engine/+/ee6a9c40492e54a0ae160293900d9e3b42b725d7
diff --git a/commits.json b/commits.json
index 71150f6..7c164f5 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"333042cf308593b7d4d121ad8f48b42460c4a401",
+  "external/github.com/flutter/engine":"ee6a9c40492e54a0ae160293900d9e3b42b725d7",
   "external/github.com/flutter/flutter":"552e74770da213b4d81a19bcbc525e1253c88753",
   "sdk":"1ffcccd9cc96ebdcf807cf8b774b1c4dd7fe5009"
 }
\ No newline at end of file