Small fixes to top level type inference.

pkg/front_end/lib/src/fasta/kernel/kernel_field_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_field_builder;
 
 import 'package:front_end/src/fasta/kernel/body_builder.dart' show BodyBuilder;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelField;
@@ skipping 97 matching lines @@
         Token token = parser.parseExpression(initializerTokenForInference);
         Expression expression = bodyBuilder.popForValue();
         bodyBuilder.checkEmpty(token.charOffset);
         initializer = expression;
       }
     }
   }
 
   @override
   DartType get builtType => field.type;
+
+  @override
+  bool get hasImplicitType => type == null;
 }