Tweak public APIs and use them in patch_sdk, dart2js, and kernel-service

pkg/front_end/lib/src/fasta/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.loader;
 
 import 'dart:async' show Future;
 
 import 'dart:collection' show Queue;
 
@@ skipping 66 matching lines @@
             fileUri = uri;
             break;
         }
       }
       LibraryBuilder library =
           target.createLibraryBuilder(uri, fileUri, isPatch);
       if (uri.scheme == "dart" && uri.path == "core") {
         coreLibrary = library;
         target.loadExtraRequiredLibraries(this);
       }
+      if (target.backendTarget.mayDefineRestrictedType(uri)) {
+        library.mayImplementRestrictedTypes = true;
+      }
       if (uri.scheme == "dart") {
         target.readPatchFiles(library);
       }
       first ??= library;
       if (library.loader == this) {
         unparsedLibraries.addLast(library);
       }
       return library;
     });
     if (accessor != null &&
@@ skipping 85 matching lines @@
   Builder getDuplicatedFieldInitializerError() {
     return target.getDuplicatedFieldInitializerError(this);
   }
 
   Builder getNativeAnnotation() => target.getNativeAnnotation(this);
 }
 
 String format(double d, int fractionDigits, int width) {
   return d.toStringAsFixed(fractionDigits).padLeft(width);
 }