Fix issues from CL 3009573002.

pkg/front_end/lib/src/fasta/source/source_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.source_library_builder;
 
 import 'package:kernel/ast.dart' show ProcedureKind;
 
 import '../../base/resolve_relative_uri.dart' show resolveRelativeUri;
 
@@ skipping 36 matching lines @@
         templateMissingPartOf,
         templatePartOfLibraryNameMismatch,
         templatePartOfUriMismatch,
         templatePartOfUseUri,
         templatePartTwice;
 
 import '../import.dart' show Import;
 
 import '../problems.dart' show unhandled;
 
+import '../util/relativize.dart' show relativizeUri;
+
 import 'source_loader.dart' show SourceLoader;
 
 abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
     extends LibraryBuilder<T, R> {
   final SourceLoader loader;
 
   final DeclarationBuilder<T> libraryDeclaration;
 
   final List<ConstructorReferenceBuilder> constructorReferences =
       <ConstructorReferenceBuilder>[];
@@ skipping 450 matching lines @@
     if (!explicitCoreImport) {
       loader.coreLibrary.exportScope.forEach((String name, Builder member) {
         addToScope(name, member, -1, true);
       });
     }
     exportScope.forEach((String name, Builder member) {
       if (member.parent != this) {
         additionalExports ??= <List<String>>[];
         Builder parent = member.parent;
         if (parent is LibraryBuilder) {
-          additionalExports.add(<String>["${parent.uri}", name]);
+          additionalExports.add(<String>[
+            relativizeUri(parent.uri, base: uri.resolve(".")),
+            name
+          ]);
         } else {
           InvalidTypeBuilder invalidType = member;
           String message = invalidType.message.message;
           additionalExports.add(<String>[null, name, message]);
         }
       }
     });
   }
 
   @override
@@ skipping 139 matching lines @@
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 
   Scope toScope(Scope parent) {
     return new Scope(members, setters, parent, isModifiable: false);
   }
 }