Refactor BackendHelpers to be reusageable with KernelWorldBuilder

pkg/compiler/lib/src/serialization/equivalence.dart

 // Copyright (c) 2016, 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.
 
 /// Functions for asserting equivalence across serialization.
 
 library dart2js.serialization.equivalence;
 
 import '../closure.dart';
 import '../common/resolution.dart';
@@ skipping 1425 matching lines @@
       return l1.isEmpty && l2.isEmpty;
     });
   }
 
   bool testTokens(
       var object1, var object2, String property, Token token1, Token token2) {
     return strategy.test(object1, object2, property, token1, token2,
         (Token t1, Token t2) {
       if (t1 == t2) return true;
       if (t1 == null || t2 == null) return false;
-      return
-          strategy.test(t1, t2, 'charOffset', t1.charOffset, t2.charOffset) &&
+      return strategy.test(
+              t1, t2, 'charOffset', t1.charOffset, t2.charOffset) &&
           strategy.test(t1, t2, 'info', t1.info, t2.info) &&
           strategy.test(t1, t2, 'value', t1.value, t2.value);
     });
   }
 
   @override
   bool visitAssert(Assert node1, Assert node2) {
     return testTokens(node1, node2, 'assertToken', node1.assertToken,
             node2.assertToken) &&
         testNodes(
@@ skipping 666 matching lines @@
 }
 
 bool areMetadataAnnotationsEquivalent(
     MetadataAnnotation metadata1, MetadataAnnotation metadata2) {
   if (metadata1 == metadata2) return true;
   if (metadata1 == null || metadata2 == null) return false;
   return areElementsEquivalent(
           metadata1.annotatedElement, metadata2.annotatedElement) &&
       areConstantsEquivalent(metadata1.constant, metadata2.constant);
 }