Compute correct return type for factory methods.

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/scanner/token.dart' show Token;
 
 import 'package:kernel/ast.dart';
 
@@ skipping 542 matching lines @@
   void addFactoryMethod(
       List<MetadataBuilder> metadata,
       int modifiers,
       ConstructorReferenceBuilder constructorNameReference,
       List<FormalParameterBuilder> formals,
       ConstructorReferenceBuilder redirectionTarget,
       int charOffset,
       int charOpenParenOffset,
       int charEndOffset,
       String nativeMethodName) {
+    KernelTypeBuilder returnType = addNamedType(
+        currentDeclaration.parent.name, <KernelTypeBuilder>[], charOffset);
     // Nested declaration began in `OutlineBuilder.beginFactoryMethod`.
     DeclarationBuilder<KernelTypeBuilder> factoryDeclaration =
         endNestedDeclaration();
     String name = constructorNameReference.name;
     String constructorName =
         computeAndValidateConstructorName(name, charOffset);
     if (constructorName != null) {
       name = constructorName;
     }
     assert(constructorNameReference.suffix == null);
     KernelProcedureBuilder procedure = new KernelProcedureBuilder(
         metadata,
         staticMask | modifiers,
-        null,
+        returnType,
         name,
         <TypeVariableBuilder>[],
         formals,
         ProcedureKind.Factory,
         this,
         charOffset,
         charOpenParenOffset,
         charEndOffset,
         nativeMethodName,
         redirectionTarget);
@@ skipping 258 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);
   }
 }