Add a warning about using a component that isn't referenced

test/testing.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.
 
 /** Common definitions used for setting up the test environment. */
 library testing;
 
 import 'package:html5lib/dom.dart';
 import 'package:html5lib/parser.dart';
 import 'package:web_ui/src/analyzer.dart';
 import 'package:web_ui/src/info.dart';
 import 'package:web_ui/src/messages.dart';
 import 'package:web_ui/src/options.dart';
 import 'package:web_ui/src/files.dart';
 import 'package:web_ui/src/file_system/path.dart';
 import 'package:web_ui/src/utils.dart';
 
 
 Document parseDocument(String html) => parse(html);
 
 Element parseSubtree(String html) => parseFragment(html).nodes[0];
 
 ElementInfo analyzeElement(Element elem, {Messages messages}) {
-  messages = messages == null ? new Messages.silent() : messages;
   var fileInfo = analyzeNodeForTesting(elem, messages: messages);
   return fileInfo.bodyInfo;
 }
 
 FileInfo analyzeDefinitionsInTree(Document doc, {Messages messages}) {
-  messages = messages == null ? new Messages.silent() : messages;
   return analyzeDefinitions(
       new SourceFile(new Path(''))..document = doc, messages: messages
   );
 }
 
 /** Parses files in [fileContents], with [mainHtmlFile] being the main file. */
 List<SourceFile> parseFiles(Map<String, String> fileContents,
     [String mainHtmlFile = 'index.html']) {
 
   var result = <SourceFile>[];
   fileContents.forEach((filename, contents) {
     var src = new SourceFile(new Path(filename));
     src.document = parse(contents);
     result.add(src);
   });
 
   return result;
 }
 
 /** Analyze all files. */
-Map<String, FileInfo> analyzeFiles(List<SourceFile> files) {
+Map<String, FileInfo> analyzeFiles(List<SourceFile> files,
+      {Messages messages}) {
+
   var result = new Map<Path, FileInfo>();
   // analyze definitions
   for (var file in files) {
-    result[file.path] = analyzeDefinitions(file);
+    result[file.path] = analyzeDefinitions(file, messages: messages);
   }
 
   // analyze file contents
   var uniqueIds = new IntIterator();
   for (var file in files) {
-    analyzeFile(file, result, uniqueIds);
+    analyzeFile(file, result, uniqueIds, messages: messages);
   }
   return _toStringMap(result);
 }
 
 Map<Path, FileInfo> toPathMap(Map<String, FileInfo> map) {
   var res = new Map<Path, FileInfo>();
   for (var k in map.keys) {
     res[new Path(k)] = map[k];
   }
   return res;
 }
 
 Map<String, FileInfo> _toStringMap(Map<Path, FileInfo> map) {
   var res = new Map<String, FileInfo>();
   for (var k in map.keys) {
     res[k.toString()] = map[k];
   }
   return res;
 }