Use Uint8List for byte lists in dart:convert.

runtime/lib/convert_patch.dart

Index: runtime/lib/convert_patch.dart
diff --git a/runtime/lib/convert_patch.dart b/runtime/lib/convert_patch.dart
index 8bd7e4001fe398a15c2004be51666a955b6d2f46..9ffef3764a1139d3fae4474d4ef5f2e990f06bfa 100644
--- a/runtime/lib/convert_patch.dart
+++ b/runtime/lib/convert_patch.dart
@@ -575,9 +575,3 @@ class _JsonParser {
     throw new FormatException(message, source, position);
   }
 }
-
-// UTF-8 conversion.
-
-patch class _Utf8Encoder {
-  /* patch */ static List<int> _createBuffer(int size) => new Uint8List(size);
-}