Update yield warnings.

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 '../constants/expressions.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
@@ skipping 1139 matching lines @@
   /// The synchronous/asynchronous marker on this function.
   AsyncMarker get asyncMarker;
 
   /// `true` if this function is external.
   bool get isExternal;
 }
 
 /// Enum for the synchronous/asynchronous function body modifiers.
 class AsyncMarker {
   /// The default function body marker.
-  static AsyncMarker SYNC = const AsyncMarker._();
+  static const AsyncMarker SYNC = const AsyncMarker._();
 
   /// The `sync*` function body marker.
-  static AsyncMarker SYNC_STAR = const AsyncMarker._(isYielding: true);
+  static const AsyncMarker SYNC_STAR = const AsyncMarker._(isYielding: true);
 
   /// The `async` function body marker.
-  static AsyncMarker ASYNC = const AsyncMarker._(isAsync: true);
+  static const AsyncMarker ASYNC = const AsyncMarker._(isAsync: true);
 
   /// The `async*` function body marker.
-  static AsyncMarker ASYNC_STAR =
+  static const AsyncMarker ASYNC_STAR =
       const AsyncMarker._(isAsync: true, isYielding: true);
 
   /// Is `true` if this marker defines the function body to have an
   /// asynchronous result, that is, either a [Future] or a [Stream].
   final bool isAsync;
 
   /// 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;
 
@@ skipping 441 matching lines @@
   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;
 }