Remember isFieldFormal informative flag in VariableDeclaration(s).

pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_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_formal_parameter_builder;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelVariableDeclaration;
 
 import '../modifier.dart' show finalMask;
@@ skipping 22 matching lines @@
       KernelLibraryBuilder compilationUnit,
       this.charOffset)
       : super(metadata, modifiers, type, name, hasThis, compilationUnit,
             charOffset);
 
   KernelVariableDeclaration get target => declaration;
 
   KernelVariableDeclaration build(SourceLibraryBuilder library) {
     if (declaration == null) {
       declaration = new KernelVariableDeclaration(name, 0,
-          type: type?.build(library), isFinal: isFinal, isConst: isConst)
+          type: type?.build(library),
+          isFinal: isFinal,
+          isConst: isConst,
+          isFieldFormal: hasThis)
         ..fileOffset = charOffset;
       if (type == null && hasThis) {
         library.loader.typeInferenceEngine
             .recordInitializingFormal(declaration);
       }
     }
     return declaration;
   }
 
   @override
   FormalParameterBuilder forFormalParameterInitializerScope() {
     assert(declaration != null);
     return !hasThis
         ? this
         : (new KernelFormalParameterBuilder(metadata, modifiers | finalMask,
             type, name, hasThis, parent, charOffset)
           ..declaration = declaration);
   }
 }