Remove uses of string + from API document generator.

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');
 
@@ skipping 59 matching lines @@
    * calling [HtmlDiff.run].
    */
   static void initialize() {
     world.getOrAddLibrary('dart:dom_deprecated');
     world.getOrAddLibrary('dart:html');
     world.process();
 
     dom = world.libraries['dart:dom_deprecated'];
   }
 
-  HtmlDiff([bool printWarnings = false]) : 
-    _printWarnings = printWarnings, 
+  HtmlDiff([bool printWarnings = false]) :
+    _printWarnings = printWarnings,
     domToHtml = new Map<Member, Set<Member>>(),
     htmlToDom = new Map<Member, Set<Member>>(),
     domTypesToHtml = new Map<Type, Set<Type>>(),
     htmlTypesToDom = new Map<Type, Set<Type>>(),
     comments = new CommentMap();
 
   void warn(String s) {
     if (_printWarnings) {
-      print('Warning: ' + s);
+      print('Warning: $s');
     }
   }
 
   /**
    * Computes the `dart:dom_deprecated` to `dart:html` mapping, and
    * places it in [domToHtml], [htmlToDom], [domTypesToHtml], and
    * [htmlTypesToDom]. Before this is run, Frog should be initialized
    * (via [parseOptions] and [initializeWorld]) and
    * [HtmlDiff.initialize] should be called.
    */
@@ skipping 22 matching lines @@
    * defining [Type].
    */
   void _addMemberDiff(Member htmlMember, List<Type> domTypes) {
     if (htmlMember.isProperty) {
       if (htmlMember.canGet) _addMemberDiff(htmlMember.getter, domTypes);
       if (htmlMember.canSet) _addMemberDiff(htmlMember.setter, domTypes);
     }
 
     var domMembers = htmlToDomMembers(htmlMember, domTypes);
     if (htmlMember == null && !domMembers.isEmpty()) {
-      warn('dart:html member ${htmlMember.declaringType.name}.' +
+      warn('dart:html member ${htmlMember.declaringType.name}.'
           '${htmlMember.name} has no corresponding dart:html member.');
     }
 
     if (htmlMember == null) return;
     if (!domMembers.isEmpty()) htmlToDom[htmlMember] = domMembers;
     domMembers.forEach((m) =>
         domToHtml.putIfAbsent(m, () => new Set()).add(htmlMember));
   }
 
   /**
@@ skipping 99 matching lines @@
   Map<String, String> _getTags(String comment) {
     if (comment == null) return const <String>{};
     final re = const RegExp("@([a-zA-Z]+) ([^;]+)(?:;|\$)");
     final tags = <String>{};
     for (var m in re.allMatches(comment.trim())) {
       tags[m[1]] = m[2];
     }
     return tags;
   }
 }