cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/collection/hash_map.dart

 part of dart.collection;
 
 bool _defaultEquals(a, b) => a == b;
 int _defaultHashCode(a) => DDC$RT.cast(a.hashCode, dynamic, int, "CastGeneral",
     """line 10, column 28 of dart:collection/hash_map.dart: """,
     a.hashCode is int, true);
 typedef bool _Equality<K>(K a, K b);
 typedef int _Hasher<K>(K object);
 abstract class HashMap<K, V> implements Map<K, V> {
-  @patch factory HashMap({bool equals(K key1, K key2), int hashCode(K key),
+  factory HashMap({bool equals(K key1, K key2), int hashCode(K key),
       bool isValidKey(potentialKey)}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
           return new _HashMap<K, V>();
         }
         hashCode = _defaultHashCode;
       } else {
         if (identical(identityHashCode, hashCode) &&
             identical(identical, equals)) {
           return new _IdentityHashMap<K, V>();
         }
         if (equals == null) {
           equals = _defaultEquals;
         }
       }
     } else {
       if (hashCode == null) {
         hashCode = _defaultHashCode;
       }
       if (equals == null) {
         equals = _defaultEquals;
       }
     }
     return new _CustomHashMap<K, V>(equals, hashCode, isValidKey);
   }
-  @patch factory HashMap.identity() = _IdentityHashMap<K, V>;
+  factory HashMap.identity() = _IdentityHashMap<K, V>;
   factory HashMap.from(Map other) {
     HashMap<K, V> result = new HashMap<K, V>();
     other.forEach((k, v) {
       result[k] = DDC$RT.cast(v, dynamic, V, "CastGeneral",
-          """line 74, column 40 of dart:collection/hash_map.dart: """, v is V,
+          """line 112, column 40 of dart:collection/hash_map.dart: """, v is V,
           false);
     });
     return result;
   }
   factory HashMap.fromIterable(Iterable iterable,
       {K key(element), V value(element)}) {
     HashMap<K, V> map = new HashMap<K, V>();
     Maps._fillMapWithMappedIterable(map, iterable, key, value);
     return map;
   }
   factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
     HashMap<K, V> map = new HashMap<K, V>();
     Maps._fillMapWithIterables(map, keys, values);
     return map;
   }
 }