Use metadata annotation @patch for patch classes

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 435224516636f1bc51b04bcda0824ede8c8b8b2f..e8b3642842f13030712f5b6c0f7bb200a15d03c4 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -7,16 +7,16 @@ const int _maxLatin1 = 0xff;
 const int _maxUtf16 = 0xffff;
 const int _maxUnicode = 0x10ffff;
 
-patch class String {
-  /* patch */ factory String.fromCharCodes(Iterable<int> charCodes,
-                                           [int start = 0, int end]) {
+@patch class String {
+  /* @patch */ factory String.fromCharCodes(Iterable<int> charCodes,
+                                            [int start = 0, int end]) {
     if (charCodes is! Iterable) throw new ArgumentError.value(charCodes, "charCodes");
     if (start is! int) throw new ArgumentError.value(start, "start");
     if (end != null && end is! int) throw new ArgumentError.value(end, "end");
     return _StringBase.createFromCharCodes(charCodes, start, end, null);
   }
 
-  /* patch */ factory String.fromCharCode(int charCode) {
+  /* @patch */ factory String.fromCharCode(int charCode) {
     if (charCode >= 0) {
       if (charCode <= 0xff) {
         return _OneByteString._allocate(1).._setAt(0, charCode);
@@ -37,8 +37,8 @@ patch class String {
     throw new RangeError.range(charCode, 0, 0x10ffff);
   }
 
-  /* patch */ const factory String.fromEnvironment(String name,
-                                                   {String defaultValue})
+  /* @patch */ const factory String.fromEnvironment(String name,
+                                                    {String defaultValue})
       native "String_fromEnvironment";
 }