Skip spurious constants in deferred computation.

pkg/compiler/lib/src/serialization/task.dart

 // Copyright (c) 2015, 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.serialization.task;
 
 import 'dart:async' show Future;
 import '../common/resolution.dart' show ResolutionImpact, ResolutionWorkItem;
 import '../common/tasks.dart' show CompilerTask;
 import '../common/work.dart' show ItemCompilationContext;
@@ skipping 16 matching lines @@
 
   DeserializerSystem deserializer;
 
   String get name => 'Serialization';
 
   /// If `true`, data must be retained to support serialization.
   // TODO(johnniwinther): Make this more precise in terms of what needs to be
   // retained, for instance impacts, resolution data etc.
   bool supportSerialization = false;
 
+  /// If `true`, deserialized data is supported.
+  bool get supportsDeserialization => deserializer != null;
+
   /// Returns the [LibraryElement] for [resolvedUri] if available from
   /// serialization.
   Future<LibraryElement> readLibrary(Uri resolvedUri) {
     if (deserializer == null) return new Future<LibraryElement>.value();
     return deserializer.readLibrary(resolvedUri);
   }
 
   /// Returns `true` if [element] has been deserialized.
   bool isDeserialized(Element element) {
     return deserializer != null && deserializer.isDeserialized(element);
@@ skipping 54 matching lines @@
 /// elements.
 abstract class DeserializerSystem {
   Future<LibraryElement> readLibrary(Uri resolvedUri);
   bool isDeserialized(Element element);
   bool hasResolvedAst(ExecutableElement element);
   ResolvedAst getResolvedAst(ExecutableElement element);
   bool hasResolutionImpact(Element element);
   ResolutionImpact getResolutionImpact(Element element);
   WorldImpact computeWorldImpact(Element element);
 }