Remove usage of dart:json.

tools/coverage.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.
 
 // This test forks a second vm process that runs a dart script as
 // a debug target, single stepping through the entire program, and
 // recording each breakpoint. At the end, a coverage map of the source
 // is printed.
 //
 // Usage: dart coverage.dart [--wire] [--verbose] target_script.dart
 //
 //   --wire      see json messages sent between the processes.
 //   --verbose   see the stdout and stderr output of the debug
 //               target process.
 
 import "dart:convert";
 import "dart:io";
-import "dart:json" as JSON;
 
 
 // Whether or not to print debug target process on the console.
 var showDebuggeeOutput = false;
 
 // Whether or not to print the debugger wire messages on the console.
 var verboseWire = false;
 
 var debugger = null;
 
@@ skipping 275 matching lines @@
   void handleMessages() {
     var msg = responses.getNextMessage();
     while (msg != null) {
       if (verboseWire) print("RECV: $msg");
       if (responses.haveGarbage()) {
         error("Error: leftover text after message: '${responses.buffer}'");
         error("Previous message may be malformed, was: '$msg'");
         cleanup();
         return;
       }
-      var msgObj = JSON.parse(msg);
+      var msgObj = JSON.decode(msg);
       handleMessage(msgObj);
       if (errorsDetected) {
         error("Error while handling message from coverage target");
         error("Message received from coverage target: $msg");
         cleanup();
         return;
       }
       if (shutdownEventSeen) {
         if (outstandingCommand != null) {
           error("Error: outstanding command when shutdown received");
@@ skipping 11 matching lines @@
         outstandingCommand = cmd;
       }
       msg = responses.getNextMessage();
     }
   }
 
   // Send a debugger command to the target VM.
   void sendMessage(Map<String,dynamic> msg) {
     assert(msg["id"] != null);
     msg["id"] = nextMessageId++;
-    String jsonMsg = JSON.stringify(msg);
+    String jsonMsg = JSON.encode(msg);
     if (verboseWire) print("SEND: $jsonMsg");
     socket.write(jsonMsg);
   }
 
   void getLineNumberTable(String url, int libId) {
     queuedCommands.add(new GetLineTableCmd(isolateId, libId, url));
   }
 
   void getLibraries() {
     queuedCommands.add(new GetLibrariesCmd(isolateId));
@@ skipping 117 matching lines @@
       return false;
     } else { 
       return char != "{";
     }
   }
 
   // Returns the character length of the next json message in the
   // buffer, or 0 if there is only a partial message in the buffer.
   // The object value must start with '{' and continues to the
   // matching '}'. No attempt is made to otherwise validate the contents
-  // as JSON. If it is invalid, a later JSON.parse() will fail.
+  // as JSON. If it is invalid, a later JSON.decode() will fail.
   int objectLength() {
     int skipWhitespace(int index) {
       while (index < buffer.length) {
         String char = buffer[index];
         if (char != " " && char != "\n" && char != "\r" && char != "\t") break;
         index++;
       }
       return index;
     }
     int skipString(int index) {
@@ skipping 44 matching lines @@
         targetOpts.add(str);
         break;
     }
   }
 
   Process.start(options.executable, targetOpts).then((Process process) {
     process.stdin.close();
     debugger = new Debugger(process);
   });
 }