Move JSSyntaxRegExp to core as a private member. This removes the last refrences to dart:coreimpl.

utils/apidoc/html_diff.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A script to assist in documenting the difference between the dart:html API
  * and the old DOM API.
  */
 library html_diff;
 
-import 'dart:coreimpl';
 import 'dart:io';
 
 // TODO(rnystrom): Use "package:" URL (#4968).
 import '../../sdk/lib/_internal/dartdoc/lib/dartdoc.dart';
 import '../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
 import '../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart';
 
 // TODO(amouravski): There is currently magic that looks at dart:* libraries
 // rather than the declared library names. This changed due to recent syntax
 // changes. We should only need to look at the library 'html'.
@@ skipping 213 matching lines @@
   Map<String, String> _getTags(String comment) {
     if (comment == null) return const <String, String>{};
     final re = new RegExp("@([a-zA-Z]+) ([^;]+)(?:;|\$)");
     final tags = <String, String>{};
     for (var m in re.allMatches(comment.trim())) {
       tags[m[1]] = m[2];
     }
     return tags;
   }
 }