Issue 28862. Implement type inference for invokeConstructor with field formal parameter.

pkg/analyzer/lib/src/task/strong_mode.dart

 // Copyright (c) 2015, 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.task.strong_mode;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
@@ skipping 221 matching lines @@
         classElement.constructors.forEach(_inferConstructorFieldFormals);
         classElement.hasBeenInferred = true;
       } finally {
         elementsBeingInferred.remove(classElement);
       }
     }
   }
 
   void _inferConstructorFieldFormals(ConstructorElement element) {
     for (ParameterElement p in element.parameters) {
-      if (p is FieldFormalParameterElement) {
+      if (p is FieldFormalParameterElementImpl) {
         _inferFieldFormalParameter(p);
       }
     }
   }
 
   /**
    * If the given [element] represents a non-synthetic instance method,
    * getter or setter, infer the return type and any parameter type(s) where
    * they were not provided.
    */
@@ skipping 115 matching lines @@
           newType = fieldElement.initializer.returnType;
         }
       }
       if (newType == null || newType.isBottom || newType.isDartCoreNull) {
         newType = typeProvider.dynamicType;
       }
       setFieldType(fieldElement, newType);
     }
   }
 
-  void _inferFieldFormalParameter(FieldFormalParameterElement element) {
+  void _inferFieldFormalParameter(FieldFormalParameterElementImpl element) {
     FieldElement field = element.field;
     if (field != null && element.hasImplicitType) {
-      (element as FieldFormalParameterElementImpl).type = field.type;
+      element.type = field.type;
     }
   }
 
   /**
    * If a parameter is covariant, any parameters that override it are too.
    */
   void _inferParameterCovariance(ParameterElementImpl parameter, int index,
       Iterable<FunctionType> overriddenTypes) {
     parameter.inheritsCovariant = overriddenTypes.any((f) {
       var param = _getCorrespondingParameter(parameter, index, f.parameters);
@@ skipping 106 matching lines @@
         results.add(element);
       }
     }
   }
 }
 
 /**
  * A class of exception that is not used anywhere else.
  */
 class _CycleException implements Exception {}