turn off app cache, print generation date at bottom

lib/dartdoc/dartdoc.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.
 
 /**
  * To generate docs for a library, run this script with the path to an
  * entrypoint .dart file, like:
  *
  *     $ dart dartdoc.dart foo.dart
  *
@@ skipping 443 matching lines @@
         ''');
   }
 
   void writeFooter() {
     writeln(
         '''
         </div>
         <div class="clear"></div>
         </div>
         ${preFooterText}
-        <div class="footer">$footerText</div>
+        <div class="footer">
+          <p>This page generated at ${new Date.now()}</p>
+          <div>$footerText</div>
+        </div>
         <script async src="${relativePath('$clientScript.js')}"></script>
         </body></html>
         ''');
   }
 
   void docIndex() {
     startFile('index.html');
 
     writeHeader(mainTitle, []);
 
@@ skipping 866 matching lines @@
       if (filename.endsWith('appcache.manifest')) {
         return;
       }
       var relativePath = filename.substring(pathPrefixLength + 1);
       write("$relativePath\n");
     };
     toCache.onDone = (done) => endFile();
     toCache.list(recursive: true);
   }
 }