Rename KernelWorldBuilder to KernelElementBuilder

tests/compiler/dart2js/dill_loader_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'dart:io';
 import 'memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/diagnostics/spannable.dart' show Spannable;
 import 'package:compiler/src/elements/entities.dart'
     show LibraryEntity, ClassEntity;
-import 'package:compiler/src/kernel/world_builder.dart';
+import 'package:compiler/src/kernel/element_map.dart';
 import 'package:compiler/src/library_loader.dart'
     show ScriptLoader, LibraryLoaderTask;
 import 'package:compiler/src/script.dart' show Script;
 import 'package:compiler/src/apiimpl.dart' show CompilerImpl;
 import "package:expect/expect.dart";
 import 'package:path/path.dart' as path;
 
 final String dartkExecutable = Platform.isWindows
     ? 'tools/dartk_wrappers/dartk.bat'
     : 'tools/dartk_wrappers/dartk';
@@ skipping 45 matching lines @@
         null,
         null,
         compiler.reporter,
         compiler.measurer);
 
     await loader.loadLibrary(entryPoint);
 
     Expect.equals(0, diagnostics.errors.length);
     Expect.equals(0, diagnostics.warnings.length);
 
-    KernelWorldBuilder worldBuilder = loader.worldBuilder;
-    LibraryEntity library = worldBuilder.lookupLibrary(uri);
+    KernelToElementMap elementMap = loader.elementMap;
+    LibraryEntity library = elementMap.lookupLibrary(uri);
     Expect.isNotNull(library);
-    ClassEntity clss = worldBuilder.lookupClass(library, 'ListLiteralTest');
+    ClassEntity clss = elementMap.lookupClass(library, 'ListLiteralTest');
     Expect.isNotNull(clss);
-    var member = worldBuilder.lookupClassMember(clss, 'testMain');
+    var member = elementMap.lookupClassMember(clss, 'testMain');
     Expect.isNotNull(member);
   });
 }