Introduce BackendImpact to separate enqueueing from data.

pkg/compiler/lib/src/common/codegen.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.common.codegen;
 
 import '../compiler.dart' show
     Compiler;
 import '../constants/values.dart' show
     ConstantValue;
@@ skipping 122 matching lines @@
 
   void registerGetOfStaticFunction(FunctionElement element) {
     world.registerGetOfStaticFunction(element);
   }
 
   void registerSelectorUse(Selector selector) {
     world.registerSelectorUse(new UniverseSelector(selector, null));
   }
 
   void registerConstSymbol(String name) {
-    backend.registerConstSymbol(name, this);
+    backend.registerConstSymbol(name);
   }
 
   void registerSpecializedGetInterceptor(Set<ClassElement> classes) {
     backend.registerSpecializedGetInterceptor(classes);
   }
 
   void registerUseInterceptor() {
     backend.registerUseInterceptor(world);
   }
 
@@ skipping 51 matching lines @@
 
   TreeElements get resolutionTree => element.resolvedAst.elements;
 
   WorldImpact run(Compiler compiler, CodegenEnqueuer world) {
     if (world.isProcessed(element)) return const WorldImpact();
 
     registry = new CodegenRegistry(compiler, resolutionTree);
     return compiler.codegen(this, world);
   }
 }