Properly resynthesize field formal parameter elements.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index cff1230be3bb446e33b27aeb19ffb3c4c9d520a6..2e781f78a3a3facc57aed6efb5e11553ff7ba551 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -2508,6 +2508,13 @@ class FieldFormalParameterElementImpl extends ParameterElementImpl
   FieldElement field;
 
   /**
+   * 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);