Rename buildOutline() and separate 'build' and 'writeProgram()'.

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 197e79915f9c88995064496b78b0b3bb6d413e83..9a51575c051ee82b4f261834ee764fe4d4acc299 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_target.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_target.dart
@@ -34,16 +34,17 @@ class DillTarget extends TargetImplementation {
     internalError("Unsupported operation.");
   }
 
-  Future<Null> writeProgram(Uri uri) {
+  @override
+  Future<Null> buildProgram() {
     return internalError("not implemented.");
   }
 
   @override
-  Future<Null> computeOutline() async {
-    if (loader.libraries.isEmpty) return null;
-    await loader.buildOutlines();
+  Future<Null> buildOutlines() async {
+    if (loader.libraries.isNotEmpty) {
+      await loader.buildOutlines();
+    }
     isLoaded = true;
-    return null;
   }
 
   DillLibraryBuilder createLibraryBuilder(Uri uri, Uri fileUri) {