don't run dart gen on JS patch code

test/dart_codegen/expect/collection/linked_hash_set.dart

Index: test/dart_codegen/expect/collection/linked_hash_set.dart
diff --git a/test/dart_codegen/expect/collection/linked_hash_set.dart b/test/dart_codegen/expect/collection/linked_hash_set.dart
index 2f866dcaf0a38c4ec27c887542968973e63484ce..21a6152db3c3d6386115257a8e1ca4a6b3b98083 100644
--- a/test/dart_codegen/expect/collection/linked_hash_set.dart
+++ b/test/dart_codegen/expect/collection/linked_hash_set.dart
@@ -1,34 +1,9 @@
 part of dart.collection;
 
 abstract class LinkedHashSet<E> implements HashSet<E> {
-  factory LinkedHashSet({bool equals(E e1, E e2), int hashCode(E e),
-      bool isValidKey(potentialKey)}) {
-    if (isValidKey == null) {
-      if (hashCode == null) {
-        if (equals == null) {
-          return new _LinkedHashSet<E>();
-        }
-        hashCode = _defaultHashCode;
-      } else {
-        if (identical(identityHashCode, hashCode) &&
-            identical(identical, equals)) {
-          return new _LinkedIdentityHashSet<E>();
-        }
-        if (equals == null) {
-          equals = _defaultEquals;
-        }
-      }
-    } else {
-      if (hashCode == null) {
-        hashCode = _defaultHashCode;
-      }
-      if (equals == null) {
-        equals = _defaultEquals;
-      }
-    }
-    return new _LinkedCustomHashSet<E>(equals, hashCode, isValidKey);
-  }
-  factory LinkedHashSet.identity() = _LinkedIdentityHashSet<E>;
+  external factory LinkedHashSet({bool equals(E e1, E e2), int hashCode(E e),
+      bool isValidKey(potentialKey)});
+  external factory LinkedHashSet.identity();
   factory LinkedHashSet.from(Iterable<E> elements) {
     LinkedHashSet<E> result = new LinkedHashSet<E>();
     for (final E element in elements) {