Add KernelWorldBuilder and KElement model.

tests/compiler/dart2js/compiler_helper.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.
 
 library compiler_helper;
 
 import 'dart:async';
 import "package:expect/expect.dart";
 
 import 'package:compiler/src/elements/elements.dart' as lego;
@@ skipping 242 matching lines @@
     final spaceRe = new RegExp('\\s+');
     regexp = regexp.replaceAll(spaceRe, '(?:\\s*)');
     if (shouldMatch) {
       Expect.isTrue(new RegExp(regexp).hasMatch(generated));
     } else {
       Expect.isFalse(new RegExp(regexp).hasMatch(generated));
     }
   });
 }
 
-
 /// Returns a 'check' function that uses comments in [test] to drive checking.
 ///
 /// The comments contains one or more 'present:' or 'absent:' tags, each
 /// followed by a quoted string. For example, the returned checker for the
 /// following text will ensure that the argument contains the three characters
 /// 'foo' and does not contain the two characters '""':
 ///
 ///    // present: "foo"
 ///    // absent:  '""'
 checkerForAbsentPresent(String test) {
   var matches = _directivePattern.allMatches(test).toList();
   checker(String generated) {
     if (matches.isEmpty) {
       Expect.fail("No 'absent:' or 'present:' directives in '$test'");
     }
     for (Match match in matches) {
       String directive = match.group(1);
       String pattern = match.groups([2, 3]).where((s) => s != null).single;
       if (directive == 'present') {
         Expect.isTrue(generated.contains(pattern),
-                      "Cannot find '$pattern' in:\n$generated");
+            "Cannot find '$pattern' in:\n$generated");
       } else {
         assert(directive == 'absent');
         Expect.isFalse(generated.contains(pattern),
-                       "Must not find '$pattern' in:\n$generated");
+            "Must not find '$pattern' in:\n$generated");
       }
     }
   }
+
   return checker;
 }
 
 RegExp _directivePattern = new RegExp(
     //      \1                     \2        \3
     r'''// *(present|absent): *(?:"([^"]*)"|'([^'']*)')''',
     multiLine: true);