Use patching for dart:io.

runtime/bin/io.dart

Index: runtime/bin/io.dart
diff --git a/runtime/bin/io.dart b/runtime/bin/io.dart
index 36d02bb268ec580cf70e5145b5e8e9153f484d9f..f260f68d80e211f454297eb0a9238633c375f7b0 100644
--- a/runtime/bin/io.dart
+++ b/runtime/bin/io.dart
@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// The dart:io library is the concatenation of all the files in
-// io_sources.gypi. This file needs to be the first file in that
-// concatenation.
+// We should be able to get rid of this file. This is used to set up
+// the dart:io library for the VM because it cannot use the actual library
+// file which is in lib/io/io.dart.
 
-#library("io");
+#library("dart:io");
 #import("dart:coreimpl");
 #import("dart:crypto");
 #import("dart:isolate");