Fix crash while inferencing instance field type.

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 3125 matching lines @@
       ResynthesizerContext context = unit.resynthesizerContext;
       for (int i = 0; i < length; i++) {
         annotations[i] = context.buildAnnotation(this, unlinkedConsts[i]);
       }
       return annotations;
     } else {
       return const <ElementAnnotation>[];
     }
   }
 
-  static int _findElementIndexUsingIdentical(List items, Object item) {
+  static int findElementIndexUsingIdentical(List items, Object item) {
     int length = items.length;
     for (int i = 0; i < length; i++) {
       if (identical(items[i], item)) {
         return i;
       }
     }
     throw new StateError('Unable to find $item in $items');
   }
 }
 
@@ skipping 1223 matching lines @@
   @override
   TypeParameterizedElementMixin get enclosingTypeParameterContext {
     return (enclosingElement as ElementImpl).typeParameterContext;
   }
 
   @override
   String get identifier {
     String identifier = super.identifier;
     Element enclosing = this.enclosingElement;
     if (enclosing is ExecutableElement) {
-      int id = ElementImpl._findElementIndexUsingIdentical(
-          enclosing.functions, this);
+      int id =
+          ElementImpl.findElementIndexUsingIdentical(enclosing.functions, this);
       identifier += "@$id";
     }
     return identifier;
   }
 
   @override
   bool get isEntryPoint {
     return isStatic && displayName == FunctionElement.MAIN_FUNCTION_NAME;
   }
 
@@ skipping 1637 matching lines @@
       return new LocalVariableElementImpl.forSerialized(
           unlinkedVariable, enclosingExecutable);
     }
   }
 
   @override
   String get identifier {
     String identifier = super.identifier;
     Element enclosing = this.enclosingElement;
     if (enclosing is ExecutableElement) {
-      int id = ElementImpl._findElementIndexUsingIdentical(
+      int id = ElementImpl.findElementIndexUsingIdentical(
           enclosing.localVariables, this);
       identifier += "@$id";
     }
     return identifier;
   }
 
   @override
   bool get isPotentiallyMutatedInClosure => true;
 
   @override
@@ skipping 2427 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }