Compute correct return type for factory methods.

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index 9a2f1084b8014cbdd94f38876830e8b7f06bd583..78dab07e078214f3e9ec896a45c9b7e55eac41fd 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -560,6 +560,8 @@ class KernelLibraryBuilder
       int charOpenParenOffset,
       int charEndOffset,
       String nativeMethodName) {
+    KernelTypeBuilder returnType = addNamedType(
+        currentDeclaration.parent.name, <KernelTypeBuilder>[], charOffset);
     // Nested declaration began in `OutlineBuilder.beginFactoryMethod`.
     DeclarationBuilder<KernelTypeBuilder> factoryDeclaration =
         endNestedDeclaration();
@@ -573,7 +575,7 @@ class KernelLibraryBuilder
     KernelProcedureBuilder procedure = new KernelProcedureBuilder(
         metadata,
         staticMask | modifiers,
-        null,
+        returnType,
         name,
         <TypeVariableBuilder>[],
         formals,