Fix InstanceFieldResolverVisitor to update element model.

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 4977 matching lines @@
       _enclosingClassDeclaration = null;
     }
   }
 
   /**
    * Resolve the instance fields in the given field declaration [node].
    */
   void _resolveFieldDeclaration(FieldDeclaration node) {
     if (!node.isStatic) {
       for (VariableDeclaration field in node.fields.variables) {
-        field.initializer?.accept(this);
+        if (field.initializer != null) {
+          field.initializer.accept(this);
+          FieldElement fieldElement = field.name.staticElement;
+          if (fieldElement.initializer != null) {
+            (fieldElement.initializer as ExecutableElementImpl).returnType =
+                field.initializer.staticType;
+          }
+        }
       }
     }
   }
 }
 
 /**
  * Instances of the class `OverrideVerifier` visit all of the declarations in a compilation
  * unit to verify that if they have an override annotation it is being used correctly.
  */
 class OverrideVerifier extends RecursiveAstVisitor<Object> {
@@ skipping 5880 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }