Introduce BackendImpact to separate enqueueing from data.

pkg/compiler/lib/src/common/backend_api.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.backend_api;
 
 import 'dart:async' show Future;
 
 import '../compiler.dart' show
     Compiler;
@@ skipping 211 matching lines @@
   void enableNoSuchMethod(Enqueuer enqueuer) {}
 
   /// Returns whether or not `noSuchMethod` support has been enabled.
   bool get enabledNoSuchMethod => false;
 
   /// Call this method to enable support for isolates.
   void enableIsolateSupport(Enqueuer enqueuer) {}
 
   void registerRequiredType(DartType type) {}
 
-  void registerConstSymbol(String name, Registry registry) {}
-  void registerNewSymbol(Registry registry) {}
+  void registerConstSymbol(String name) {}
 
   bool isNullImplementation(ClassElement cls) {
     return cls == compiler.nullClass;
   }
 
   ClassElement get intImplementation => compiler.intClass;
   ClassElement get doubleImplementation => compiler.doubleClass;
   ClassElement get numImplementation => compiler.numClass;
   ClassElement get stringImplementation => compiler.stringClass;
   ClassElement get listImplementation => compiler.listClass;
@@ skipping 151 matching lines @@
   /// Returns the constant expression of [node], or `null` if [node] is not
   /// a constant expression.
   ConstantExpression getConstant(Node node);
 
   /// Registers [type] as instantiated.
   void registerInstantiatedType(InterfaceType type);
 
   /// Resolves [typeName] to a type in the context of [node].
   DartType resolveTypeFromString(Node node, String typeName);
 }