Only attempt to do type inference on fields that lack a declared type.

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 446 matching lines @@
         metadata: metadata,
         name: name,
         typeVariables: typeVariables,
         modifiers: modifiers,
         interfaces: interfaces,
         charOffset: charOffset);
     checkTypeVariables(typeVariables, supertype.builder);
   }
 
   @override
-  void addField(List<MetadataBuilder> metadata, int modifiers,
-      KernelTypeBuilder type, String name, int charOffset, Token initializer) {
+  void addField(
+      List<MetadataBuilder> metadata,
+      int modifiers,
+      KernelTypeBuilder type,
+      String name,
+      int charOffset,
+      Token initializerTokenForInference,
+      bool hasInitializer) {
     addBuilder(
         name,
-        new KernelFieldBuilder(
-            metadata, type, name, modifiers, this, charOffset, initializer),
+        new KernelFieldBuilder(metadata, type, name, modifiers, this,
+            charOffset, initializerTokenForInference, hasInitializer),
         charOffset);
   }
 
   String computeAndValidateConstructorName(String name, int charOffset) {
     String className = currentDeclaration.name;
     bool startsWithClassName = name.startsWith(className);
     if (startsWithClassName && name.length == className.length) {
       // Unnamed constructor or factory.
       return "";
     }
@@ skipping 366 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);
   }
 }