Support deserialized compilation of the empty program.

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 36 matching lines @@
   }
 
   /// Creates the [ResolutionWorkItem] for the deserialized [element].
   ResolutionWorkItem createResolutionWorkItem(
       Element element, ItemCompilationContext context) {
     assert(deserializer != null);
     assert(isDeserialized(element));
     return new DeserializedResolutionWorkItem(
         element, context, deserializer.computeWorldImpact(element));
   }
+
+  bool hasResolvedAst(Element element) {
+    return deserializer != null ? deserializer.hasResolvedAst(element) : false;
+  }
+
+  ResolvedAst getResolvedAst(Element element) {
+    return deserializer != null ? deserializer.getResolvedAst(element) : null;
+  }
 }
 
 /// A [ResolutionWorkItem] for a deserialized element.
 ///
 /// This will not resolve the element but only compute the [WorldImpact].
 class DeserializedResolutionWorkItem implements ResolutionWorkItem {
   final Element element;
   final ItemCompilationContext compilationContext;
   final WorldImpact worldImpact;
   bool _isAnalyzed = false;
@@ skipping 10 matching lines @@
     world.registerProcessedElement(element);
     return worldImpact;
   }
 }
 
 /// The interface for a system that supports deserialization of libraries and
 /// elements.
 abstract class DeserializerSystem {
   Future<LibraryElement> readLibrary(Uri resolvedUri);
   bool isDeserialized(Element element);
+  bool hasResolvedAst(Element element);
   ResolvedAst getResolvedAst(Element element);
   ResolutionImpact getResolutionImpact(Element element);
   WorldImpact computeWorldImpact(Element element);
 }