Mark outline as external

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

Index: pkg/front_end/lib/src/fasta/fasta.dart
diff --git a/pkg/front_end/lib/src/fasta/fasta.dart b/pkg/front_end/lib/src/fasta/fasta.dart
index ce753f7c6af2a4c60baaa3aed037ff752ea2c666..279963c54facf249e8a7f322370e44c0c5fd84b6 100644
--- a/pkg/front_end/lib/src/fasta/fasta.dart
+++ b/pkg/front_end/lib/src/fasta/fasta.dart
@@ -147,6 +147,7 @@ class CompileTask {
       deprecated_inputError(uri, -1, "Unexpected input: $uri");
     }
     await dillTarget.buildOutlines();
+    dillTarget.loader.libraries.forEach((lib) => lib.isExternal = true);
     var outline = await kernelTarget.buildOutlines();
     if (c.options.dumpIr && output != null) {
       printProgramText(outline, libraryFilter: kernelTarget.isSourceLibrary);