Fix some issues in element serialization.

pkg/compiler/lib/src/elements/elements.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 elements;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
 import '../compiler.dart' show Compiler;
 import '../constants/constructors.dart';
@@ skipping 1088 matching lines @@
 }
 
 abstract class FunctionSignature {
   FunctionType get type;
   List<FormalElement> get requiredParameters;
   List<FormalElement> get optionalParameters;
 
   int get requiredParameterCount;
   int get optionalParameterCount;
   bool get optionalParametersAreNamed;
-  FormalElement get firstOptionalParameter;
   bool get hasOptionalParameters;
 
   int get parameterCount;
   List<FormalElement> get orderedOptionalParameters;
 
   void forEachParameter(void function(FormalElement parameter));
   void forEachRequiredParameter(void function(FormalElement parameter));
   void forEachOptionalParameter(void function(FormalElement parameter));
 
   void orderedForEachParameter(void function(FormalElement parameter));
@@ skipping 69 matching lines @@
 
   /// Is `true` if this marker defines the function body to have a plural
   /// result, that is, either an [Iterable] or a [Stream].
   final bool isYielding;
 
   const AsyncMarker._({this.isAsync: false, this.isYielding: false});
 
   String toString() {
     return '${isAsync ? 'async' : 'sync'}${isYielding ? '*' : ''}';
   }
+
+  /// Canonical list of marker values.
+  ///
+  /// Added to make [AsyncMarker] enum-like.
+  static const List<AsyncMarker> values =
+      const <AsyncMarker>[SYNC, SYNC_STAR, ASYNC, ASYNC_STAR];
+
+
+  /// Index to this marker within [values].
+  ///
+  /// Added to make [AsyncMarker] enum-like.
+  int get index => values.indexOf(this);
 }
 
 /// A top level, static or instance function.
 abstract class MethodElement extends FunctionElement implements MemberElement {}
 
 /// A local function or closure (anonymous local function).
 abstract class LocalFunctionElement extends FunctionElement
     implements LocalElement {}
 
 /// A constructor.
@@ skipping 556 matching lines @@
   /// by a field.
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }