Refactor BackendHelpers to be reusageable with KernelWorldBuilder

pkg/compiler/lib/src/elements/elements.dart

 // Copyright (c) 2012, 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 elements;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
 import '../constants/constructors.dart';
 import '../constants/expressions.dart';
@@ skipping 725 matching lines @@
     Uri aUri = a.script.readableUri;
     Uri bUri = b.script.readableUri;
     return '${aUri}'.compareTo('${bUri}');
   }
 
   static List<Element> sortedByPosition(Iterable<Element> elements) {
     return elements.toList()..sort(compareByPosition);
   }
 
   static bool isFixedListConstructorCall(
-      Element element, Send node, CommonElements commonElements) {
-    return element == commonElements.unnamedListConstructor &&
+      ConstructorEntity element, Send node, CommonElements commonElements) {
+    return commonElements.isUnnamedListConstructor(element) &&
         node.isCall &&
         !node.arguments.isEmpty &&
         node.arguments.tail.isEmpty;
   }
 
   static bool isGrowableListConstructorCall(
-      Element element, Send node, CommonElements commonElements) {
-    return element == commonElements.unnamedListConstructor &&
+      ConstructorEntity element, Send node, CommonElements commonElements) {
+    return commonElements.isUnnamedListConstructor(element) &&
         node.isCall &&
         node.arguments.isEmpty;
   }
 
   static bool isFilledListConstructorCall(
-      Element element, Send node, CommonElements commonElements) {
-    return element == commonElements.filledListConstructor &&
+      ConstructorEntity element, Send node, CommonElements commonElements) {
+    return commonElements.isFilledListConstructor(element) &&
         node.isCall &&
         !node.arguments.isEmpty &&
         !node.arguments.tail.isEmpty &&
         node.arguments.tail.tail.isEmpty;
   }
 
   static bool isConstructorOfTypedArraySubclass(
       Element element, ClosedWorld closedWorld) {
     if (closedWorld.commonElements.typedDataLibrary == null) return false;
     if (!element.isConstructor) return false;
@@ skipping 1242 matching lines @@
   /// by a field.
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }