Add FunctionEntity.asyncMarker and refactor SourceInformationStrategy to avoid ResolvedAst

pkg/compiler/lib/src/resolution/signatures.dart

 // Copyright (c) 2014, 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.resolution.signatures;
 
 import '../common.dart';
 import '../common/resolution.dart';
 import '../elements/resolution_types.dart';
 import '../elements/elements.dart';
+import '../elements/entities.dart' show AsyncMarker;
 import '../elements/modelx.dart'
     show
         ErroneousFieldElementX,
         ErroneousInitializingFormalElementX,
         FormalElementX,
         FunctionSignatureX,
         InitializingFormalElementX,
         LocalParameterElementX,
         TypeVariableElementX;
 import '../elements/names.dart';
@@ skipping 483 matching lines @@
 /// variables of the function signature itself when its signature is analyzed.
 class FunctionSignatureBuildingScope extends TypeVariablesScope {
   @override
   final List<ResolutionDartType> typeVariables;
 
   FunctionSignatureBuildingScope(Scope parent, this.typeVariables)
       : super(parent);
 
   String toString() => 'FunctionSignatureBuildingScope($typeVariables)';
 }