Refactor BackendHelpers to be reusageable with KernelWorldBuilder

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

Index: pkg/compiler/lib/src/serialization/equivalence.dart
diff --git a/pkg/compiler/lib/src/serialization/equivalence.dart b/pkg/compiler/lib/src/serialization/equivalence.dart
index 56ec19723c52fc59cc66816d54cfe86b893405d4..3fd3f451a665029061a93ba5cbba20e11e7b4290 100644
--- a/pkg/compiler/lib/src/serialization/equivalence.dart
+++ b/pkg/compiler/lib/src/serialization/equivalence.dart
@@ -1443,8 +1443,8 @@ class NodeEquivalenceVisitor implements Visitor1<bool, Node> {
         (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);
     });