Remove usage of dart:json.

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:convert";
 import "dart:io";
-import "dart:json" as json;
 import "dart:async";
 
 
 Map<int, Completer> outstandingCommands;
 
 Socket vmSock;
 String vmData;
 var stdinSubscription;
 var vmSubscription;
 int seqNum = 0;
@@ skipping 41 matching lines @@
   vmSock.close();
   stdinSubscription.cancel();
 }
 
 
 Future sendCmd(Map<String, dynamic> cmd) {
   var completer = new Completer();
   int id = cmd["id"];
   outstandingCommands[id] = completer;
   if (verbose) {
-    print("sending: '${json.stringify(cmd)}'");
+    print("sending: '${JSON.encode(cmd)}'");
   }
-  vmSock.write(json.stringify(cmd));
+  vmSock.write(JSON.encode(cmd));
   return completer.future;
 }
 
 void processCommand(String cmdLine) {
   
   void huh() {
     print("'$cmdLine' not understood, try h for help");
   }
 
   seqNum++;
@@ skipping 370 matching lines @@
   } else {
     assert(reason == "exception");
     var excObj = msg["params"]["exception"];
     print("Isolate $isolate_id paused on exception");
     print(remoteObject(excObj));
   }
 }
 
 
 void processVmMessage(String jsonString) {
-  var msg = json.parse(jsonString);
+  var msg = JSON.decode(jsonString);
   if (msg == null) {
     return;
   }
   var event = msg["event"];
   if (event == "paused") {
     handlePausedEvent(msg);
     return;
   }
   if (event == "breakpointResolved") {
     Map params = msg["params"];
@@ skipping 157 matching lines @@
       process.stdin.close();
       process.exitCode.then((int exitCode) {
         print('${arguments.join(" ")} exited with $exitCode');
       });
       debuggerMain();
     });
   } else {
     debuggerMain();
   }
 }