Don't copy Int8Arrays when passing them in as lists of bytes and don't

sdk/lib/io/common.dart

Index: sdk/lib/io/common.dart
diff --git a/sdk/lib/io/common.dart b/sdk/lib/io/common.dart
index 687d2edf036bd6b84d31939a38c2aab8b76d6085..5a39a46652f771508b7c11b8688bf0d4c993d9dc 100644
--- a/sdk/lib/io/common.dart
+++ b/sdk/lib/io/common.dart
@@ -68,7 +68,9 @@ class _BufferAndOffset {
 // benefit that it is faster to access from the C code as well.
 _BufferAndOffset _ensureFastAndSerializableBuffer(
     List buffer, int offset, int bytes) {
-  if (buffer is Uint8List || _BufferUtils._isBuiltinList(buffer)) {
+  if (buffer is Uint8List ||
+      buffer is Int8List ||
+      _BufferUtils._isBuiltinList(buffer)) {
     return new _BufferAndOffset(buffer, offset);
   }
   var newBuffer = new Uint8List(bytes);