Replace ClosedWorld.backend with ClosedWorld.backendClasses

pkg/compiler/lib/src/compiler.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 dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 832 matching lines @@
       });
 
   void processQueue(Enqueuer world, Element main) =>
       selfTask.measureSubtask("Compiler.processQueue", () {
         world.nativeEnqueuer.processNativeClasses(libraryLoader.libraries);
         if (main != null && !main.isMalformed) {
           FunctionElement mainMethod = main;
           mainMethod.computeType(resolution);
           if (mainMethod.functionSignature.parameterCount != 0) {
             // The first argument could be a list of strings.
-            backend.listImplementation.ensureResolved(resolution);
+            backend.backendClasses.listImplementation
+                .ensureResolved(resolution);
             backend.registerInstantiatedType(
-                backend.listImplementation.rawType, world, globalDependencies);
-            backend.stringImplementation.ensureResolved(resolution);
+                backend.backendClasses.listImplementation.rawType,
+                world,
+                globalDependencies);
+            backend.backendClasses.stringImplementation
+                .ensureResolved(resolution);
             backend.registerInstantiatedType(
-                backend.stringImplementation.rawType,
+                backend.backendClasses.stringImplementation.rawType,
                 world,
                 globalDependencies);
 
             backend.registerMainHasArguments(world);
           }
           world.addToWorkList(main);
         }
         if (options.verbose) {
           progress.reset();
         }
@@ skipping 1372 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }