Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/sourcemaps/sourcemap_html_helper.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.
 
 /// Helper for creating HTML visualization of the source map information
 /// generated by a [SourceMapProcessor].
 
 library sourcemap.html.helper;
 
 import 'dart:convert';
@@ skipping 409 matching lines @@
 $jsTrace
 </div>
 ''');
   }
   return jsTraceBuffer.toString();
 }
 
 /// Computes the HTML information for the [info].
 SourceMapHtmlInfo createHtmlInfo(
     SourceLocationCollection collection, SourceMapInfo info) {
-  js.Node node = info.node;
-  String code = info.code;
   String name = info.name;
   SourceLocationCollection subcollection =
       new SourceLocationCollection(collection);
   CodeProcessor codeProcessor = new CodeProcessor(name, subcollection);
   for (js.Node node in info.nodeMap.nodes) {
     info.nodeMap[node]
         .forEach((int targetOffset, List<SourceLocation> sourceLocations) {
       for (SourceLocation sourceLocation in sourceLocations) {
         codeProcessor.addSourceLocation(targetOffset, sourceLocation);
       }
@@ skipping 178 matching lines @@
       String dartCode = truncate(codePoint.dartCode, 50);
       buffer.write('<td class="code">${dartCode}</td>');
       buffer.write('<td>${escape(codePoint.sourceLocation.shortText)}</td>');
     }
     buffer.write('</tr>');
   });
   buffer.write('</table>');
 
   return buffer.toString();
 }