Use JSON.stringify to serialize debugger messages

test/mjsunit/mirror-function.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 26 matching lines @@
 }
 
 MirrorRefCache.prototype.lookup = function(handle) {
   return this.refs_[handle];
 }
 
 function testFunctionMirror(f) {
   // Create mirror and JSON representation.
   var mirror = debug.MakeMirror(f);
   var serializer = debug.MakeMirrorSerializer();
-  var json = serializer.serializeValue(mirror);
-  var refs = new MirrorRefCache(serializer.serializeReferencedObjects());
+  var json = JSON.stringify(serializer.serializeValue(mirror));
+  var refs = new MirrorRefCache(
+      JSON.stringify(serializer.serializeReferencedObjects()));
 
   // Check the mirror hierachy.
   assertTrue(mirror instanceof debug.Mirror);
   assertTrue(mirror instanceof debug.ValueMirror);
   assertTrue(mirror instanceof debug.ObjectMirror);
   assertTrue(mirror instanceof debug.FunctionMirror);
 
   // Check the mirror properties.
   assertTrue(mirror.isFunction());
   assertEquals('function', mirror.type());
@@ skipping 21 matching lines @@
 
   // Check the formatted text (regress 1142074).
   assertEquals(f.toString(), fromJSON.text);
 }
 
 
 // Test a number of different functions.
 testFunctionMirror(function(){});
 testFunctionMirror(function a(){return 1;});
 testFunctionMirror(Math.sin);