Remove Encoding-enum from dart:io and add interface in dart:convert.

tests/standalone/debugger/debug_lib.dart

 // 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:async";
 import "dart:convert";
@@ skipping 375 matching lines @@
 
   // Data collected from debug target.
   Map currentMessage = null;  // Currently handled message sent by target.
   String scriptUrl = null;
   bool shutdownEventSeen = false;
   int isolateId = 0;
   bool isPaused = false;
 
   Debugger(this.targetProcess, this.script) {
     var stdoutStringStream = targetProcess.stdout
-        .transform(new StringDecoder())
+        .transform(UTF8.decoder)
         .transform(new LineSplitter());
     stdoutStringStream.listen((line) {
       print("TARG: $line");
       if (line.startsWith("Debugger listening")) {
         RegExp portExpr = new RegExp(r"\d+");
         var port = portExpr.stringMatch(line);
         print("Debug target found listening at port '$port'");
         openConnection(int.parse(port));
       }
     });
 
     var stderrStringStream = targetProcess.stderr
-        .transform(new StringDecoder())
+        .transform(UTF8.decoder)
         .transform(new LineSplitter());
     stderrStringStream.listen((line) {
       print("TARG: $line");
     });
   }
 
   // Handle debugger events, updating the debugger state.
   void handleEvent(Map<String,dynamic> msg) {
     events.add(new Event(msg));
     
@@ skipping 115 matching lines @@
 
   // Record error message.
   void error(String s) {
     errors.add(s);
   }
 
   void openConnection(int portNumber) {
     Socket.connect("127.0.0.1", portNumber).then((s) {
         s.setOption(SocketOption.TCP_NODELAY, true);
         this.socket = s;
-        var stringStream = socket.transform(new StringDecoder());
+        var stringStream = socket.transform(UTF8.decoder);
         stringStream.listen((str) {
             try {
               responses.append(str);
               handleMessages();
             } catch(e, trace) {
               print("Unexpected exception:\n$e\n$trace");
               cleanup();
             }
           },
           onDone: () {
@@ skipping 60 matching lines @@
   targetOpts.add("--debuggee");
   print('args: ${targetOpts.join(" ")}');
 
   Process.start(Platform.executable, targetOpts).then((Process process) {
     print("Debug target process started, pid ${process.pid}.");
     process.stdin.close();
     var debugger = new Debugger(process, new DebugScript(script));
   });
   return true;
 }