don't run dart gen on JS patch code

test/dart_codegen/expect/core/identical.dart

Index: test/dart_codegen/expect/core/identical.dart
diff --git a/test/dart_codegen/expect/core/identical.dart b/test/dart_codegen/expect/core/identical.dart
index 1f398d4f5be4894946688ad6091625769368125d..5a91d55d60af44d9662812c431a0cbd83eedc323 100644
--- a/test/dart_codegen/expect/core/identical.dart
+++ b/test/dart_codegen/expect/core/identical.dart
@@ -1,10 +1,4 @@
 part of dart.core;
 
-bool identical(Object a, Object b) {
-  return ((__x22) => DDC$RT.cast(__x22, dynamic, bool, "CastGeneral",
-      """line 11, column 10 of dart:core/identical.dart: """, __x22 is bool,
-      true))(Primitives.identicalImplementation(a, b));
-}
-int identityHashCode(Object object) => ((__x23) => DDC$RT.cast(__x23, dynamic,
-    int, "CastGeneral", """line 23, column 40 of dart:core/identical.dart: """,
-    __x23 is int, true))(objectHashCode(object));
+external bool identical(Object a, Object b);
+external int identityHashCode(Object object);