Update ddbg.dart for async and json changes

tools/ddbg.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.
 
 // Simple interactive debugger shell that connects to the Dart VM's debugger
 // connection port.
 
 import "dart:io";
-import "dart:json";
+import "dart:json" as json;
 import "dart:utf";
+import "dart:async";
 
 
 Map<int, Completer> outstandingCommands;
 
 Socket vmSock;
 String vmData;
 OutputStream vmStream;
 int seqNum = 0;
 int isolate_id = -1;
 
@@ skipping 38 matching lines @@
   vmSock.close();
   stdin.close();
 }
 
 
 Future sendCmd(Map<String, dynamic> cmd) {
   var completer = new Completer();
   int id = cmd["id"];
   outstandingCommands[id] = completer;
   if (verbose) {
-    print("sending: '${jsonStringify(cmd)}'");
+    print("sending: '${json.stringify(cmd)}'");
   }
-  vmStream.writeString(jsonStringify(cmd));
+  vmStream.writeString(json.stringify(cmd));
   return completer.future;
 }
 
 
 void processCommand(String cmdLine) {
   seqNum++;
   var args = cmdLine.split(' ');
   if (args.length == 0) {
     return;
   }
@@ skipping 321 matching lines @@
     assert(reason == "exception");
     var excObj = msg["params"]["exception"];
     print("Isolate $isolate_id paused on exception");
     print(remoteObject(excObj));
   }
   print("Stack trace:");
   printStackTrace(stackTrace);
 }
 
 
-void processVmMessage(String json) {
-  var msg = parseJson(json);
+void processVmMessage(String jsonString) {
+  var msg = json.parse(jsonString);
   if (msg == null) {
     return;
   }
   var event = msg["event"];
   if (event == "paused") {
     handlePausedEvent(msg);
     return;
   }
   if (event == "breakpointResolved") {
     Map params = msg["params"];
@@ skipping 138 matching lines @@
       // are coming from the debugger, and which errors are coming
       // from the process being debugged.
       process.stderr.pipe(stdout);
       process.stdout.pipe(stdout);
       debuggerMain();
     });
   } else {
     debuggerMain();
   }
 }