Add flutter mode to patched_sdk

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

Index: pkg/front_end/lib/src/fasta/dill/dill_loader.dart
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_loader.dart b/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
index b8537da9d2caddddad36a36cc7d434ac0bbf364a..11a3951898e5020ea2de75e7a79054065ba735d6 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
@@ -35,6 +35,8 @@ class DillLoader extends Loader<Library> {
   }
 
   Future<Null> buildOutline(DillLibraryBuilder builder) async {
+    assert(builder.library != null,

[Siggi Cherem (dart-lang), 2017/06/08 22:18:53]

(platched_sdk often fails here when files are not found, this helps debug the
underlying issue.)

[ahe, 2017/06/09 09:23:35]

Please use internalError.

[Siggi Cherem (dart-lang), 2017/06/14 17:55:37]

Done.

+        "Builder.library for ${builder.uri} should not be null");
     builder.library.classes.forEach(builder.addClass);
     builder.library.procedures.forEach(builder.addMember);
     builder.library.typedefs.forEach(builder.addTypedef);