Refactor LibraryUpdater to prepare for parts.

dart/tests/try/web/incremental_compilation_update_test.dart

 // Copyright (c) 2014, 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.
 
 library trydart.incremental_compilation_update_test;
 
 import 'dart:html' hide
     Element;
 
 import 'dart:async' show
@@ skipping 1920 matching lines @@
   for (String text in splitLines(code)) {
     PreElement line = new PreElement()
         ..appendText(text.trimRight())
         ..classes.add("line");
     result.append(line);
   }
 
   return result;
 }
 
-
 StyleElement lineNumberStyle() {
   StyleElement style = new StyleElement()..appendText('''
 h2, h3 {
   color: black;
 }
 
 .output {
   padding: 0px;
   counter-reset: line-number;
   padding-bottom: 1em;
@@ skipping 12 matching lines @@
   position: absolute;
   left: 0px;
   width: 3em;
   text-align: right;
   background-color: lightgoldenrodyellow;
 }
 ''');
   style.type = 'text/css';
   return style;
 }