Use ByteArray's native for Socket and File.

runtime/bin/socket_impl.dart

Index: runtime/bin/socket_impl.dart
===================================================================
--- runtime/bin/socket_impl.dart	(revision 3621)
+++ runtime/bin/socket_impl.dart	(working copy)
@@ -309,12 +309,14 @@
       // When using the Dart C API access to ObjectArray by index is
       // currently much faster. This function will make a copy of the
       // supplied List to an ObjectArray if it isn't already.
-      ObjectArray outBuffer;
+      List<int> outBuffer;

[cshapiro, 2012/01/27 23:00:04]

I think this can safely be retyped as a ByteArray even if the enclosing method
typed to return a List<int>, similar to how ObjectArray is used now.

[Anders Johnsen, 2012/01/27 23:42:39]

The thing is, that both a ByteArray and an ObjectArray can be assigned to
outBuffer, List<int> being the common ancestor. 

       int outOffset = offset;
       if (buffer is ObjectArray) {
         outBuffer = buffer;
+      } else if (buffer is ByteArray) {
+        outBuffer = buffer;
       } else {
-        outBuffer = new ObjectArray(bytes);
+        outBuffer = new ByteArray(bytes);
         outOffset = 0;
         int j = offset;
         for (int i = 0; i < bytes; i++) {