Added ability to make library_list be JSON instead of YAML

pkg/docgen/lib/docgen.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.
 
 /**
  * **docgen** is a tool for creating machine readable representations of Dart
  * code metadata, including: classes, members, comments and annotations.
  *
  * docgen is run on a `.dart` file or a directory containing `.dart` files.
  *
@@ skipping 230 matching lines @@
   entityMap.values.where((e) => e is Class).forEach((c) => c.makeValid());
   // Everything is a subclass of Object, therefore empty the list to avoid a
   // giant list of subclasses to be printed out.
   if (parseSdk) entityMap['dart.core.Object'].subclasses.clear();
 
   var filteredEntities = entityMap.values.where(_isVisible);
   // Output libraries and classes to file after all information is generated.
   filteredEntities.where((e) => e is Class || e is Library).forEach((output) {
     _writeIndexableToFile(output, outputToYaml);
   });
-  // Outputs a yaml file with all libraries and their preview comments after 
-  // creating all libraries. This will help the viewer know what libraries are 
-  // available to read in.
+  // Outputs a YAML or JSON file with all libraries and their preview comments 
+  // after creating all libraries. This will help the viewer know what 
+  // libraries are available to read in.
   var libraryMap = {
     'libraries' : filteredEntities.where((e) => 
         e is Library).map((e) => e.previewMap).toList(),
     'introduction' : introduction == '' ? 
         '' : markdown.markdownToHtml(new File(introduction).readAsStringSync(),
             linkResolver: linkResolver, inlineSyntaxes: markdownSyntaxes)
   };
-  _writeToFile(getYamlString(libraryMap), 'library_list.yaml', append: append);
+  if (outputToYaml) {
+    _writeToFile(getYamlString(libraryMap), 'library_list.yaml', 
+        append: append);
+  } else {
+    _writeToFile(stringify(libraryMap), 'library_list.json', append: append);
+  }
   // Outputs all the qualified names documented with their type.
   // This will help generate search results.
   _writeToFile(filteredEntities.map((e) => 
       '${e.qualifiedName} ${e.typeName}').join('\n'),
       'index.txt', append: append);
 }
 
 Library generateLibrary(dart2js.Dart2JsLibraryMirror library) {
   _currentLibrary = library;
   var result = new Library(library.qualifiedName, _commentToHtml(library),
@@ skipping 877 matching lines @@
   String qualifiedName;
   List<String> parameters;
 
   Annotation(this.qualifiedName, this.parameters);
 
   Map toMap() => {
     'name': qualifiedName,
     'parameters': parameters
   };
 }