Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/patch_parser.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.
 
 /**
  * This library contains the infrastructure to parse and integrate patch files.
  *
  * Three types of elements can be patched: [LibraryElement], [ClassElement],
  * [FunctionElement]. Patches are introduced in patch libraries which are loaded
  * together with the corresponding origin library. Which libraries that are
@@ skipping 393 matching lines @@
       Compiler compiler, Element element, MetadataAnnotation annotation) {
     return getPatchVersion(annotation);
   }
 
   @override
   void validate(Compiler compiler, Element element,
       MetadataAnnotation annotation, ConstantValue constant) {
     ResolutionDartType annotationType =
         constant.getType(compiler.commonElements);
     if (annotationType.element !=
-        compiler.backend.helpers.patchAnnotationClass) {
+        compiler.commonElements.patchAnnotationClass) {
       DiagnosticReporter reporter = compiler.reporter;
       reporter.internalError(annotation, 'Invalid patch annotation.');
     }
   }
 }
 
 void tryPatchGetter(
     DiagnosticReporter reporter, Element origin, FunctionElement patch) {
   if (!origin.isAbstractField) {
     reporter.reportError(
@@ skipping 102 matching lines @@
 
 class PatchVersion {
   final String tag;
 
   const PatchVersion(this.tag);
 
   bool isActive(String patchTag) => tag == null || tag == patchTag;
 
   String toString() => 'PatchVersion($tag)';
 }