Test for immutable Lists in ListSet API methods.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index a0997502203dd42f80b6f8b629de78a6ee726d19..5717ec81b21fca221195dc0b94be6426d557ba4d 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1244,6 +1244,9 @@ DART_EXPORT Dart_Handle Dart_ListSetAsBytes(Dart_Handle list,
   DARTSCOPE(isolate);
   const Object& obj = Object::Handle(Api::UnwrapHandle(list));
   if (obj.IsArray()) {
+    if (obj.IsImmutableArray()) {
+      return Api::Error("Cannot modify immutable array");
+    }
     Array& array_obj = Array::Handle();
     array_obj ^= obj.raw();
     Integer& integer = Integer::Handle();
@@ -1289,6 +1292,9 @@ DART_EXPORT Dart_Handle Dart_ListSetAt(Dart_Handle list,
   DARTSCOPE(isolate);
   const Object& obj = Object::Handle(Api::UnwrapHandle(list));
   if (obj.IsArray()) {
+    if (obj.IsImmutableArray()) {
+      return Api::Error("Cannot modify immutable array");
+    }
     Array& array_obj = Array::Handle();
     array_obj ^= obj.raw();
     const Object& value_obj = Object::Handle(Api::UnwrapHandle(value));