fixes #25482, flatten Futures in strong mode so Future.then works

pkg/analyzer/lib/src/dart/element/element.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.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2490 matching lines @@
  * [FieldElement] associated with the parameter.
  */
 class FieldFormalParameterElementImpl extends ParameterElementImpl
     implements FieldFormalParameterElement {
   /**
    * The field associated with this field formal parameter.
    */
   FieldElement field;
 
   /**
+   * Initialize a newly created parameter element to have the given [name].
+   */
+  FieldFormalParameterElementImpl(Identifier name) : super.forNode(name);
+
+  /**
    * Initialize a newly created parameter element to have the given [name] and
    * [offset].
    */
   FieldFormalParameterElementImpl.forNameAndOffset(String name, int nameOffset)
       : super(name, nameOffset);
 
-  /**
-   * Initialize a newly created parameter element to have the given [name].
-   */
-  FieldFormalParameterElementImpl(Identifier name) : super.forNode(name);
-
   @override
   bool get isInitializingFormal => true;
 
   @override
   accept(ElementVisitor visitor) =>
       visitor.visitFieldFormalParameterElement(this);
 }
 
 /**
  * A concrete implementation of a [FunctionElement].
@@ skipping 564 matching lines @@
       }
     }
     this._imports = imports;
   }
 
   @override
   bool get isBrowserApplication =>
       entryPoint != null && isOrImportsBrowserLibrary;
 
   @override
+  bool get isDartAsync => name == "dart.async";
+
+  @override
   bool get isDartCore => name == "dart.core";
 
   @override
   bool get isInSdk =>
       StringUtilities.startsWith5(name, 0, 0x64, 0x61, 0x72, 0x74, 0x2E);
 
   /**
    * Return `true` if the receiver directly or indirectly imports the
    * 'dart:html' libraries.
    */
@@ skipping 1479 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }