Introduce BackendImpact to separate enqueueing from data.

pkg/compiler/lib/src/resolution/registry.dart

 // Copyright (c) 2014, 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.resolution.registry;
 
 import '../common/backend_api.dart' show
     Backend,
     ForeignResolver;
 import '../common/resolution.dart' show
@@ skipping 650 matching lines @@
 
   void registerInstantiatedType(InterfaceType type) {
     worldImpact.registerInstantiatedType(type);
     mapping.addRequiredType(type);
   }
 
   void registerAbstractClassInstantiation() {
     worldImpact.registerFeature(Feature.ABSTRACT_CLASS_INSTANTIATION);
   }
 
-  void registerNewSymbol() {
-    worldImpact.registerFeature(Feature.NEW_SYMBOL);
-  }
-
   void registerRequiredType(DartType type, Element enclosingElement) {
     worldImpact.registerRequiredType(type);
     mapping.addRequiredType(type);
   }
 
   void registerStringInterpolation() {
     worldImpact.registerFeature(Feature.STRING_INTERPOLATION);
   }
 
   void registerFallThroughError() {
@@ skipping 101 matching lines @@
   @override
   void registerInstantiatedType(InterfaceType type) {
     registry.registerInstantiatedType(type);
   }
 
   @override
   DartType resolveTypeFromString(Node node, String typeName) {
     return visitor.resolveTypeFromString(node, typeName);
   }
 }