[dart2wasm] Fix JSCM string type in assertion strings

Change-Id: I09b410d0cee4e8190746e454d2ab1bcf0c87f5d1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/361168
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
diff --git a/pkg/dart2wasm/lib/code_generator.dart b/pkg/dart2wasm/lib/code_generator.dart
index 31c40e1..9e76d40 100644
--- a/pkg/dart2wasm/lib/code_generator.dart
+++ b/pkg/dart2wasm/lib/code_generator.dart
@@ -1106,8 +1106,11 @@
         b.ref_null(w.HeapType.none);
       }
       final Location? location = node.location;
+      final stringClass = translator.options.jsCompatibility
+          ? translator.jsStringClass
+          : translator.stringBaseClass;
       final w.RefType stringRefType =
-          translator.classInfo[translator.stringBaseClass]!.nullableType;
+          translator.classInfo[stringClass]!.nullableType;
       if (location != null) {
         translator.constants.instantiateConstant(
           function,