Add a way to use shared CanonicalName root to deserialize Program.

pkg/front_end/lib/src/fasta/dill/dill_target.dart

Index: pkg/front_end/lib/src/fasta/dill/dill_target.dart
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_target.dart b/pkg/front_end/lib/src/fasta/dill/dill_target.dart
index 4dc805a04e79ceae053a27df5b24a9e9b752aec5..e88b01f4b6948e45de97d7c36e6a12f63868a5a3 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_target.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_target.dart
@@ -6,27 +6,24 @@ library fasta.dill_target;
 
 import 'dart:async' show Future;
 
-import 'package:kernel/ast.dart' show Class;
-
-import 'dill_loader.dart' show DillLoader;
+import 'package:kernel/ast.dart' show CanonicalName, Class;
 
 import '../errors.dart' show internalError;
-
+import '../kernel/kernel_builder.dart' show ClassBuilder;
 import '../target_implementation.dart' show TargetImplementation;
-
 import '../ticker.dart' show Ticker;
-
 import '../translate_uri.dart' show TranslateUri;
-
-import '../kernel/kernel_builder.dart' show ClassBuilder;
-
 import 'dill_library_builder.dart' show DillLibraryBuilder;
+import 'dill_loader.dart' show DillLoader;
 
 class DillTarget extends TargetImplementation {
+  /// The name root that is shared between all targets.
+  final CanonicalName nameRoot;
+
   bool isLoaded = false;
   DillLoader loader;
 
-  DillTarget(Ticker ticker, TranslateUri uriTranslator)
+  DillTarget(this.nameRoot, Ticker ticker, TranslateUri uriTranslator)
       : super(ticker, uriTranslator) {
     loader = new DillLoader(this);
   }
@@ -45,7 +42,7 @@ class DillTarget extends TargetImplementation {
   }
 
   Future<Null> writeOutline(Uri uri) async {
-    if (loader.program == null) return null;
+    if (loader.libraries.isEmpty) return null;
     await loader.buildOutlines();
     isLoaded = true;
     return null;