Move json to lib/json/{json.dart, json_frog.dart}

frog/reader.dart

 // Copyright (c) 2011, 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.
 
 /**
  * An code reader that abstracts away the distinction between internal and user
  * libraries.
  */
 class LibraryReader {
   Map _specialLibs;
   LibraryReader() {
     if (options.config == 'dev') {
       _specialLibs = {
         'dart:core': joinPaths(options.libDir, 'corelib.dart'),
         'dart:coreimpl': joinPaths(options.libDir, 'corelib_impl.dart'),
         'dart:html': joinPaths(options.libDir,
             '../../client/html/release/html.dart'),
         'dart:htmlimpl': joinPaths(options.libDir,
             '../../client/html/release/htmlimpl.dart'),
         'dart:dom': joinPaths(options.libDir,
             '../../client/dom/frog/dom_frog.dart'),
-        'dart:json': joinPaths(options.libDir, 'json_frog.dart'),
+        'dart:json': joinPaths(options.libDir, '../../lib/json/json_frog.dart'),
       };
     } else if (options.config == 'sdk') {
       _specialLibs = {
         'dart:core': joinPaths(options.libDir, 'core/core_frog.dart'),
         'dart:coreimpl': joinPaths(options.libDir, 
           'coreimpl/coreimpl_frog.dart'),
         'dart:html': joinPaths(options.libDir, 'html/html.dart'),
         'dart:htmlimpl': joinPaths(options.libDir, 'htmlimpl/htmlimpl.dart'),
         'dart:dom': joinPaths(options.libDir, 'dom/frog/dom_frog.dart'),
-        'dart:json': joinPaths(options.libDir, 'json/json_frog.dart'),
+        'dart:json': joinPaths(options.libDir, '../../lib/json/json_frog.dart'),
       };
     } else {
       world.error('Invalid configuration ${options.config}');
     }
   }
 
   SourceFile readFile(String fullname) {
     var filename = _specialLibs[fullname];
     if (filename == null) {
       filename = fullname;
     }
 
     if (world.files.fileExists(filename)) {
       // TODO(jimhug): Should we cache these based on time stamps here?
       return new SourceFile(filename, world.files.readAll(filename));
     } else {
       world.error('File not found: $filename', null);
       return new SourceFile(filename, '');
     }
   }
 }