pkg/compiler: fix imports

pkg/compiler/lib/src/js_backend/backend.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 js_backend.backend;
 
 import 'dart:async' show Future;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
@@ skipping 52 matching lines @@
         TransformedWorldImpact,
         WorldImpact,
         WorldImpactVisitor;
 import '../util/util.dart';
 import '../world.dart' show ClassWorld;
 import 'backend_helpers.dart';
 import 'backend_impact.dart';
 import 'backend_serialization.dart' show JavaScriptBackendSerialization;
 import 'checked_mode_helpers.dart';
 import 'codegen/task.dart';
-
 import 'constant_handler_javascript.dart';
 import 'custom_elements_analysis.dart';
 import 'js_interop_analysis.dart' show JsInteropAnalysis;
 import 'lookup_map_analysis.dart' show LookupMapAnalysis;
 import 'namer.dart';
 import 'native_data.dart' show NativeData;
 import 'no_such_method_registry.dart';
 import 'patch_resolver.dart';
 import 'type_variable_handler.dart';
 
@@ skipping 3125 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }