Introduce WorldImpact

pkg/compiler/lib/src/dart_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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 111 matching lines @@
       classElement.ensureResolved(compiler);
     }
     // Enqueue the methods that the VM might invoke on user objects because
     // we don't trust the resolution to always get these included.
     world.registerInvocation(new Selector.call("toString", null, 0));
     world.registerInvokedGetter(new Selector.getter("hashCode", null));
     world.registerInvocation(new Selector.binaryOperator("=="));
     world.registerInvocation(new Selector.call("compareTo", null, 1));
   }
 
-  void codegen(CodegenWorkItem work) { }
+  WorldImpact codegen(CodegenWorkItem work) => const WorldImpact();
 
   static bool checkTreeIntegrity(tree_ir.RootNode node) {
     new CheckTreeIntegrity().check(node);
     return true; // So this can be used from assert().
   }
 
   static bool checkCpsIntegrity(cps_ir.RootNode node) {
     new CheckCpsIntegrity().check(node);
     return true; // So this can be used from assert().
   }
@@ skipping 415 matching lines @@
   }
 
   void traceGraph(String title, var irObject) {
     compiler.tracer.traceGraph(title, irObject);
   }
 
   DartTypes get dartTypes => compiler.types;
 
   InternalErrorFunction get internalError => compiler.internalError;
 }