Add FunctionEntity.asyncMarker and refactor SourceInformationStrategy to avoid ResolvedAst

pkg/compiler/lib/src/typechecker.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.typechecker;
 
 import 'common/names.dart' show Identifiers;
 import 'common/resolution.dart' show Resolution;
 import 'common/tasks.dart' show CompilerTask;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart';
 import 'constants/values.dart';
 import 'common_elements.dart';
 import 'elements/resolution_types.dart';
 import 'elements/elements.dart'
     show
         AbstractFieldElement,
         AstElement,
-        AsyncMarker,
         ClassElement,
         ConstructorElement,
         Element,
         Elements,
         EnumClassElement,
         EnumConstantElement,
         ExecutableElement,
         FieldElement,
         FunctionElement,
         GetterElement,
         InitializingFormalElement,
         LibraryElement,
         MemberSignature,
         ParameterElement,
         ResolvedAst,
         SetterElement,
         TypeDeclarationElement,
         TypedElement,
         VariableElement;
+import 'elements/entities.dart' show AsyncMarker;
 import 'elements/names.dart';
 import 'enqueue.dart' show DeferredAction;
 import 'resolution/class_members.dart' show MembersCreator, ErroneousMember;
 import 'resolution/tree_elements.dart' show TreeElements;
 import 'tree/tree.dart';
 import 'util/util.dart' show Link, LinkBuilder;
 
 class TypeCheckerTask extends CompilerTask {
   final Compiler compiler;
   TypeCheckerTask(Compiler compiler)
@@ skipping 2007 matching lines @@
 
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     reporter.internalError(node,
         'Unexpected node ${node.getObjectDescription()} in the type checker.');
   }
 }