Add flutter mode to patched_sdk

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

 // Copyright (c) 2016, 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 fasta.dill_loader;
 
 import 'dart:async' show Future;
 
 import 'package:kernel/ast.dart' show Library, Program;
 
@@ skipping 17 matching lines @@
         libraries.add(library);
         DillLibraryBuilder builder = read(library.importUri, -1);
         builder.library = library;
         builders.add(builder);
       }
     }
     return builders;
   }
 
   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);
     builder.library.fields.forEach(builder.addMember);
   }
 
   Future<Null> buildBody(DillLibraryBuilder builder) {
     return buildOutline(builder);
   }
 }