don't run dart gen on JS patch code

test/dart_codegen/expect/collection/hash_map.dart

Index: test/dart_codegen/expect/collection/hash_map.dart
diff --git a/test/dart_codegen/expect/collection/hash_map.dart b/test/dart_codegen/expect/collection/hash_map.dart
index dce0c7ced636f651fbbdd0c1c7780389b6ea356b..919504d7d9d124698c09656b34b16b9f13f73b50 100644
--- a/test/dart_codegen/expect/collection/hash_map.dart
+++ b/test/dart_codegen/expect/collection/hash_map.dart
@@ -7,39 +7,14 @@ int _defaultHashCode(a) => DDC$RT.cast(a.hashCode, dynamic, int, "CastGeneral",
 typedef bool _Equality<K>(K a, K b);
 typedef int _Hasher<K>(K object);
 abstract class HashMap<K, V> implements Map<K, V> {
-  factory HashMap({bool equals(K key1, K key2), int hashCode(K key),
-      bool isValidKey(potentialKey)}) {
-    if (isValidKey == null) {
-      if (hashCode == null) {
-        if (equals == null) {
-          return new _HashMap<K, V>();
-        }
-        hashCode = _defaultHashCode;
-      } else {
-        if (identical(identityHashCode, hashCode) &&
-            identical(identical, equals)) {
-          return new _IdentityHashMap<K, V>();
-        }
-        if (equals == null) {
-          equals = _defaultEquals;
-        }
-      }
-    } else {
-      if (hashCode == null) {
-        hashCode = _defaultHashCode;
-      }
-      if (equals == null) {
-        equals = _defaultEquals;
-      }
-    }
-    return new _CustomHashMap<K, V>(equals, hashCode, isValidKey);
-  }
-  factory HashMap.identity() = _IdentityHashMap<K, V>;
+  external factory HashMap({bool equals(K key1, K key2), int hashCode(K key),
+      bool isValidKey(potentialKey)});
+  external factory HashMap.identity();
   factory HashMap.from(Map other) {
     HashMap<K, V> result = new HashMap<K, V>();
     other.forEach((k, v) {
       result[k] = DDC$RT.cast(v, dynamic, V, "CastGeneral",
-          """line 112, column 40 of dart:collection/hash_map.dart: """, v is V,
+          """line 87, column 40 of dart:collection/hash_map.dart: """, v is V,
           false);
     });
     return result;