fix issues caught by analysis_server

lib/runtime/messages_widget.dart

 // Copyright (c) 2015, 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.
 
 /// This library provides a single function called injectLogs which when called
 /// will request a logs json file and build a small widget out of them which
 /// groups the logs by level.
 library polymer.build.log_injector;
 
-import 'dart:async';
 import 'dart:convert';
 import 'dart:html';
 
-import 'package:path/path.dart' as path;
 import 'package:source_span/source_span.dart';
 import 'package:dev_compiler/src/summary.dart';
 
 main() async {
   await window.animationFrame;
   displayMessages(await HttpRequest.getString('messages.json'));
 }
 
 void displayMessages(String data) {
   var summary = GlobalSummary.parse(JSON.decode(data));
@@ skipping 29 matching lines @@
       var message = _hyperlinkUrls(_escape(m.message));
       var span = m.span;
       var sb = new StringBuffer();
       sb.write('<div class="message"><div class="text $level">$message</div>');
       if (span != null) {
         sb.write('<div class="location">'
             '  <span class="location">${span.start.toolString}</span></div>'
             '  <span class="text">');
         if (span is SourceSpanWithContext) {
           var context = span.context;
-          var text = span.text;
           sb.write(_escape(context.substring(0, span.start.column)));
           sb.write('<span class="$level">');
           sb.write(_escape(span.text));
           sb.write('</span>');
           sb.write(_escape(context.substring(span.end.column)));
         } else {
           sb.write(_escape(span.text));
         }
         sb.write('</span></div></div>');
       }
@@ skipping 51 matching lines @@
 class _Visitor extends RecursiveSummaryVisitor {
   final Map<String, List<MessageSummary>> messagesByLevel = {};
 
   @override
   void visitMessage(MessageSummary message) {
     var level = message.level.toLowerCase();
     messagesByLevel.putIfAbsent(level, () => []);
     messagesByLevel[level].add(message);
   }
 }