Use patching for dart:io.

runtime/bin/builtin.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 #ifndef BIN_BUILTIN_H_
 #define BIN_BUILTIN_H_
 
 #include <stdio.h>
 #include <stdlib.h>
 
@@ skipping 28 matching lines @@
   static Dart_Handle LoadAndCheckLibrary(BuiltinLibraryId id);
   static void PrintString(FILE* out, Dart_Handle object);
 
  private:
   static Dart_NativeFunction NativeLookup(Dart_Handle name,
                                           int argument_count);
 
   static const char builtin_source_[];
   static const char crypto_source_[];
   static const char io_source_[];
+  static const char io_patch_[];
   static const char json_source_[];
   static const char uri_source_[];
   static const char utf_source_[];
   static const char web_source_[];
 
   typedef struct {
     const char* url_;
     const char* source_;
+    const char* patch_url_;
+    const char* patch_source_;
     bool has_natives_;
   } builtin_lib_props;
   static builtin_lib_props builtin_libraries_[];
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Builtin);
 };
 
 
 #endif  // BIN_BUILTIN_H_