[kernel] Fix binary.md specification of Extensions

Fixes #40629

Change-Id: If458df641553d84c7a75aa51698145b22183c3d6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135901
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
diff --git a/pkg/kernel/binary.md b/pkg/kernel/binary.md
index 2762192..b6ff1da 100644
--- a/pkg/kernel/binary.md
+++ b/pkg/kernel/binary.md
@@ -352,7 +352,7 @@
 enum ExtensionMemberKind { Field = 0, Method = 1, Getter = 2, Setter = 3, Operator = 4, TearOff = 5, }
 
 type ExtensionMemberDescriptor {
-  StringReference name;
+  Name name;
   ExtensionMemberKind kind;
   Byte flags (isStatic);
   MemberReference member;