Issue 21850. Fix for incremental resolving field formal parameters.

pkg/analyzer/test/generated/incremental_resolver_test.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 engine.incremental_resolver_test;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
@@ skipping 1921 matching lines @@
     _resolveUnit(r'''
 class A {
   int f;
   A(int a, int b) {
     f = a + b;
   }
 }''');
     _resolve(_editString('+', '*'), _isFunctionBody);
   }
 
+  void test_constructor_fieldFormalParameter() {
+    _resolveUnit(r'''
+class A {
+  int xy;
+  A(this.x);
+}''');
+    _resolve(_editString('this.x', 'this.xy'), _isDeclaration);
+  }
+
   void test_constructor_fieldInitializer_add() {
     _resolveUnit(r'''
 class A {
   int f;
   A(int a, int b);
 }''');
     _resolve(_editString(');', ') : f = a + b;'), _isClassMember);
   }
 
   void test_constructor_fieldInitializer_edit() {
@@ skipping 2085 matching lines @@
   }
 
   @override
   visitYieldStatement(YieldStatement node) {
     YieldStatement other = this.other;
     _visitNode(node.expression, other.expression);
   }
 
   void _verifyElement(Element a, Element b) {
     if (a != b) {
+      print(a.location);
+      print(b.location);
       fail('Expected: $b\n  Actual: $a');
     }
     if (a == null && b == null) {
       return;
     }
     if (a.nameOffset != b.nameOffset) {
       fail('Expected: ${b.nameOffset}\n  Actual: ${a.nameOffset}');
     }
   }
 
@@ skipping 51 matching lines @@
     _visitList(node.metadata, other.metadata);
     _visitNode(node.identifier, other.identifier);
   }
 
   static void assertSameResolution(CompilationUnit actual,
       CompilationUnit expected) {
     _SameResolutionValidator validator = new _SameResolutionValidator(expected);
     actual.accept(validator);
   }
 }