Store parts in Kernel Library, resynthesize parts in Analyzer.

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.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.kernel_library_builder;
 
 import 'package:front_end/src/fasta/dill/dill_library_builder.dart';
 import 'package:front_end/src/fasta/combinator.dart' as fasta;
 import 'package:front_end/src/fasta/export.dart';
 import 'package:front_end/src/fasta/import.dart';
@@ skipping 741 matching lines @@
         importedLibrary = importedBuilder.library;
       } else if (importedBuilder is KernelLibraryBuilder) {
         importedLibrary = importedBuilder.library;
       }
       if (importedLibrary != null) {
         library.addDependency(new LibraryDependency.import(importedLibrary,
             name: import.prefix,
             combinators: toKernelCombinators(import.combinators)));
       }
     }
+
     for (Export export in exports) {
       var exportedBuilder = export.exported;
       Library exportedLibrary;
       if (exportedBuilder is DillLibraryBuilder) {
         exportedLibrary = exportedBuilder.library;
       } else if (exportedBuilder is KernelLibraryBuilder) {
         exportedLibrary = exportedBuilder.library;
       }
       if (exportedLibrary != null) {
         library.addDependency(new LibraryDependency.export(exportedLibrary,
             combinators: toKernelCombinators(export.combinators)));
       }
     }
+
+    for (var part in parts) {
+      // TODO(scheglov): Add support for annotations, see
+      // https://github.com/dart-lang/sdk/issues/30284.
+      String fileUri = part.fileUri.toString();
+      library.addPart(new LibraryPart(<Expression>[], fileUri));
+    }
+
     library.name = name;
     library.procedures.sort(compareProcedures);
     return library;
   }
 
   @override
   Builder buildAmbiguousBuilder(
       String name, Builder builder, Builder other, int charOffset,
       {bool isExport: false, bool isImport: false}) {
     // TODO(ahe): Can I move this to Scope or Prefix?
@@ skipping 153 matching lines @@
           mixinApplicationClasses.putIfAbsent(name, () => builder);
       if (existing != builder) {
         part.scope.local.remove(name);
       }
     });
     super.includePart(part);
     nativeMethods.addAll(part.nativeMethods);
     boundlessTypeVariables.addAll(part.boundlessTypeVariables);
   }
 }