Use Uint8List for byte lists in dart:convert.

sdk/lib/convert/byte_conversion.dart

Index: sdk/lib/convert/byte_conversion.dart
diff --git a/sdk/lib/convert/byte_conversion.dart b/sdk/lib/convert/byte_conversion.dart
index bb94991fefc9aee9498a1c4aaf75fb80bc338152..d27b40fcf89bba5b2cb4ee34e39bfe4dc0f045c4 100644
--- a/sdk/lib/convert/byte_conversion.dart
+++ b/sdk/lib/convert/byte_conversion.dart
@@ -78,8 +78,7 @@ class _ByteCallbackSink extends ByteConversionSinkBase {
   static const _INITIAL_BUFFER_SIZE = 1024;
 
   final _ChunkedConversionCallback<List<int>> _callback;
-  // TODO(11971, floitsch): use Uint8List instead of normal lists.
-  List<int> _buffer = new List<int>(_INITIAL_BUFFER_SIZE);
+  List<int> _buffer = new Uint8List(_INITIAL_BUFFER_SIZE);
   int _bufferIndex = 0;
 
   _ByteCallbackSink(void callback(List<int> accumulated))
@@ -91,8 +90,7 @@ class _ByteCallbackSink extends ByteConversionSinkBase {
       // Grow the buffer.
       int oldLength = _buffer.length;
       int newLength = _roundToPowerOf2(chunk.length + oldLength) * 2;
-      // TODO(11971, floitsch): use Uint8List instead of normal lists.
-      List<int> grown = new List<int>(newLength);
+      List<int> grown = new Uint8List(newLength);
       grown.setRange(0, _buffer.length, _buffer);
       _buffer = grown;
     }