Update dart:io to convert strings between UTF8 and current code page

runtime/bin/platform.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_PLATFORM_H_
 #define BIN_PLATFORM_H_
 
 #include "bin/builtin.h"
 
 class Platform {
  public:
   // Perform platform specific initialization.
   static bool Initialize();
 
   // Returns the number of processors on the machine.
   static int NumberOfProcessors();
 
   // Returns a string representing the operating system ("linux",
   // "macos" or "windows"). The returned string should not be
   // deallocated by the caller.
   static const char* OperatingSystem();
 
   // Returns a string representation of an error code. The returned
   // string must be deallocated by the caller.
   static char* StrError(int error_code);
 
   // Extracts the local hostname.
   static bool LocalHostname(char* buffer, intptr_t buffer_length);
 
-  // Extracts the environment variables for the current process.
-  // The array of strings returned must be deallocated using
-  // delete[]. The number of elements in the array is returned
+  // Extracts the environment variables for the current process.  The
+  // array of strings returned must be deallocated using
+  // FreeEnvironment. The number of elements in the array is returned
   // in the count argument.
   static char** Environment(intptr_t* count);
+  static void FreeEnvironment(char** env, intptr_t count);
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Platform);
 };
 
 #endif  // BIN_PLATFORM_H_