Add FrontEndStrategy, ResolutionFrontEndStrategy and KernelFrontEndStrategy

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/common_elements.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/library_loader.dart'
-    show ScriptLoader, LibraryLoaderTask;
+    show ScriptLoader, DillLibraryLoaderTask;
 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';
 
 /// Run the dartk.dart script, and return the binary encoded results.
@@ skipping 26 matching lines @@
     Uri entryPoint = Uri.parse('memory:main.dill');
     List<int> kernelBinary = runDartk(filename);
 
     CompilerImpl compiler = compilerFor(
         entryPoint: entryPoint,
         memorySourceFiles: {'main.dill': kernelBinary},
         diagnosticHandler: diagnostics,
         outputProvider: output,
         options: ['--read-dill']);
     await compiler.setupSdk();
-    dynamic loader = new LibraryLoaderTask(
-        true,
-        compiler.resolvedUriTranslator,
-        new TestScriptLoader(compiler),
-        null,
-        null,
-        null,
-        null,
-        null,
-        compiler.reporter,
-        compiler.measurer);
-
-    await loader.loadLibrary(entryPoint);
+    await compiler.libraryLoader.loadLibrary(entryPoint);
 
     Expect.equals(0, diagnostics.errors.length);
     Expect.equals(0, diagnostics.warnings.length);
 
-    KernelWorldBuilder worldBuilder = loader.worldBuilder;
-    LibraryEntity library = worldBuilder.lookupLibrary(uri);
+    ElementEnvironment environment = compiler.elementEnvironment;
+    LibraryEntity library = environment.lookupLibrary(uri);
     Expect.isNotNull(library);
-    ClassEntity clss = worldBuilder.lookupClass(library, 'ListLiteralTest');
+    ClassEntity clss = environment.lookupClass(library, 'ListLiteralTest');
     Expect.isNotNull(clss);
-    var member = worldBuilder.lookupClassMember(clss, 'testMain');
+    var member = environment.lookupClassMember(clss, 'testMain');
     Expect.isNotNull(member);
   });
 }