Add FunctionEntity.asyncMarker and refactor SourceInformationStrategy to avoid ResolvedAst

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 '../elements/elements.dart'
-    show AsyncMarker, ClassElement, LocalFunctionElement;
+import '../elements/elements.dart' show ClassElement, LocalFunctionElement;
 import '../elements/entities.dart';
 import '../elements/types.dart' show DartType, InterfaceType;
 import '../universe/use.dart' show ConstantUse, DynamicUse, StaticUse, TypeUse;
 import '../universe/world_impact.dart'
     show WorldImpact, WorldImpactBuilderImpl, WorldImpactVisitor;
 import '../util/enumset.dart';
 import '../util/util.dart' show Pair, Setlet;
 import 'work.dart' show WorkItem;
 
 class CodegenImpact extends WorldImpact {
@@ skipping 149 matching lines @@
 
   void registerAsyncMarker(AsyncMarker asyncMarker) {
     worldImpact.registerAsyncMarker(asyncMarker);
   }
 }
 
 /// [WorkItem] used exclusively by the [CodegenEnqueuer].
 abstract class CodegenWorkItem extends WorkItem {
   CodegenRegistry get registry;
 }