Generate docgen file names with hyphens in their names instead of colons

pkg/docgen/test/inherited_comments_test.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.test.inherited_comments;
 
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 10 matching lines @@
   });
 
   test('inherited comments', () {
     schedule(() {
       var codeDir = getMultiLibraryCodePath();
       expect(FileSystemEntity.isDirectorySync(codeDir), isTrue);
       return dg.docgen([codeDir], out: p.join(d.defaultRoot, 'docs'));
     });
 
     schedule(() {
-      var path = p.join(d.defaultRoot, 'docs', 'dart:core.Set.json');
+      var path = p.join(d.defaultRoot, 'docs', 'dart-core.Set.json');
       var dartCoreSetJson = new File(path).readAsStringSync();
 
       var dartCoreSet = JSON.decode(dartCoreSetJson) as Map<String, dynamic>;
 
       var toListDetails = dartCoreSet['inheritedMethods']['methods']['toList']
           as Map<String, dynamic>;
 
       expect(toListDetails, containsPair('comment', _TO_LIST_COMMENT));
       expect(toListDetails, containsPair('commentFrom', _TO_LIST_COMMENT_FROM));
     });
   });
 }
 
 const _TO_LIST_COMMENT = "<p>Creates a <a>dart:core.List</a> containing the "
     "elements of this <a>dart:core.Iterable</a>.</p>\n<p>The elements are in "
     "iteration order. The list is fixed-length\nif "
     "<a>dart:core.Set.toList.growable</a> is false.</p>";
 const _TO_LIST_COMMENT_FROM = "dart:core.Iterable.toList";