Add function parameter info in docgen.

pkg/docgen/lib/src/models/method.dart

 // Copyright (c) 2014, 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.
 
 library docgen.models.method;
 
 import 'package:markdown/markdown.dart' as markdown;
 
 import '../exports/mirrors_util.dart' as dart2js_util;
 import '../exports/source_mirrors.dart';
@@ skipping 135 matching lines @@
         markdown.markdownToHtml(unresolvedComment.trim(),
             linkResolver: fixReference, inlineSyntaxes: MARKDOWN_SYNTAXES);
       commentInheritedFrom = comment != '' ?
           methodInheritedFrom.commentInheritedFrom : '';
       result = comment;
     }
     return result;
   }
 
   bool isValidMirror(DeclarationMirror mirror) => mirror is MethodMirror;
-}
+}