Fix deprecation warnings in dart:io. Now completely warning free.

sdk/lib/io/common.dart

 // 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.
 
 part of dart.io;
 
 // Constants used when working with native ports.
 const int _SUCCESS_RESPONSE = 0;
 const int _ILLEGAL_ARGUMENT_RESPONSE = 1;
 const int _OSERROR_RESPONSE = 2;
@@ skipping 10 matching lines @@
 class OSError {
   /** Constant used to indicate that no OS error code is available. */
   static const int noErrorCode = -1;
 
   /** Creates an OSError object from a message and an errorCode. */
   const OSError([String this.message = "", int this.errorCode = noErrorCode]);
 
   /** Converts an OSError object to a string representation. */
   String toString() {
     StringBuffer sb = new StringBuffer();
-    sb.add("OS Error");
+    sb.write("OS Error");
     if (!message.isEmpty) {
-      sb.add(": ");
-      sb.add(message);
+      sb.write(": ");
+      sb.write(message);
       if (errorCode != noErrorCode) {
-        sb.add(", errno = ");
-        sb.add(errorCode.toString());
+        sb.write(", errno = ");
+        sb.write(errorCode.toString());
       }
     } else if (errorCode != noErrorCode) {
-      sb.add(": errno = ");
-      sb.add(errorCode.toString());
+      sb.write(": errno = ");
+      sb.write(errorCode.toString());
     }
     return sb.toString();
   }
 
   /**
     * Error message supplied by the operating system. null if no message is
     * associated with the error.
     */
   final String message;
 
@@ skipping 38 matching lines @@
 
 
 // TODO(ager): The only reason for the class here is that
 // we cannot patch a top-level function.
 class _BufferUtils {
   // Check if a List is a builtin VM List type. Returns true
   // if the List is a builtin VM List type and false if it is
   // a user defined List type.
   external static bool _isBuiltinList(List buffer);
 }