- Allow implementations to hook into the Utf8Decoder.convert method.

runtime/lib/convert_patch.dart

Index: runtime/lib/convert_patch.dart
===================================================================
--- runtime/lib/convert_patch.dart	(revision 43026)
+++ runtime/lib/convert_patch.dart	(working copy)
@@ -30,6 +30,13 @@
     // TODO(lrn): Recognize a fused decoder where the next step is JsonDecoder.
     return super.fuse(next);
   }
+
+  // Allow intercepting of UTF8 decoding when builtin lists are passed.
+  /* patch */
+  static String _convertIntercepted(
+      bool allowMalformed, List<int> codeUnits, int start, int end) {
+    return null;  // This call was not intercepted.
+  }
 }
 
 class _JsonUtf8Decoder extends Converter<List<int>, Object> {