Make IOSink implement StringSink

tests/standalone/debugger/debug_lib.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2013, 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.
 
 // Library used by debugger wire protocol tests (standalone VM debugging).
 
 library DartDebugger;
 
 import "dart:io";
 import "dart:utf";
 import "dart:json" as JSON;
@@ skipping 441 matching lines @@
 
   runScript(List entries) {
     script = new DebugScript(entries);
     openConnection();
   }
 
   // Send a debugger command to the target VM.
   void sendMessage(Map<String,dynamic> msg) {
     String jsonMsg = JSON.stringify(msg);
     if (verboseWire) print("SEND: $jsonMsg");
-    socket.addString(jsonMsg);
+    socket.write(jsonMsg);
   }
 
   bool get errorsDetected => errors.length > 0;
 
   // Record error message.
   void error(String s) {
     errors.add(s);
   }
 
   void openConnection() {
@@ skipping 58 matching lines @@
     process.exitCode.then((int exitCode) {
       Expect.equals(0, exitCode);
       Expect.equals(0, exitCode);
       print("Debug target process exited with exit code $exitCode");
     });
     var debugger = new Debugger(process, debugPort);
     debugger.runScript(script);
   });
   return true;
 }