Perform type inference on explicitly typed fields.

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;
 
 import 'package:front_end/src/fasta/parser/parser.dart' show Parser;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 import 'package:front_end/src/fasta/builder/class_builder.dart'
     show ClassBuilder;
 
 import 'package:front_end/src/fasta/source/source_library_builder.dart'
     show SourceLibraryBuilder;
 
 import 'package:front_end/src/fasta/type_inference/type_inference_listener.dart'
     show TypeInferenceListener;
 
-import 'package:kernel/ast.dart' show Expression, Field, Name;
+import 'package:kernel/ast.dart' show DartType, Expression, Field, Name;
 
 import 'kernel_builder.dart'
     show Builder, FieldBuilder, KernelTypeBuilder, MetadataBuilder;
 
 class KernelFieldBuilder extends FieldBuilder<Expression> {
   final Field field;
   final List<MetadataBuilder> metadata;
   final KernelTypeBuilder type;
   final Token initializerToken;
 
@@ skipping 51 matching lines @@
           library.uri,
           typeInferrer,
           fieldDependencies: typeInferenceEngine.getFieldDependencies(field));
       Parser parser = new Parser(bodyBuilder);
       Token token = parser.parseExpression(initializerToken);
       Expression expression = bodyBuilder.popForValue();
       bodyBuilder.checkEmpty(token.charOffset);
       initializer = expression;
     }
   }
+
+  @override
+  DartType get builtType => field.type;
 }