Extract InterceptorData from JavaScriptBackend.

pkg/compiler/lib/src/js_backend/backend_helpers.dart

 // Copyright (c) 2015, 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 dart2js.js_backend.helpers;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Uris;
 import '../compiler.dart' show Compiler;
 import '../core_types.dart' show CommonElements, ElementEnvironment;
@@ skipping 25 matching lines @@
   static const String START_ROOT_ISOLATE = 'startRootIsolate';
 
   static const String JS = 'JS';
   static const String JS_BUILTIN = 'JS_BUILTIN';
   static const String JS_EMBEDDED_GLOBAL = 'JS_EMBEDDED_GLOBAL';
   static const String JS_INTERCEPTOR_CONSTANT = 'JS_INTERCEPTOR_CONSTANT';
 
   final ElementEnvironment _env;
 
   // TODO(johnniwinther): Remove this.
-  final JavaScriptBackend backend;
+  final JavaScriptBackend _backend;
 
   final CommonElements commonElements;
 
-  BackendHelpers(this._env, this.backend, this.commonElements);
+  BackendHelpers(this._env, this._backend, this.commonElements);
 
   ClassEntity _findInterceptorsClass(String name) =>
       _findClass(interceptorsLibrary, name);
 
   FunctionEntity _findInterceptorsFunction(String name) =>
       _findLibraryMember(interceptorsLibrary, name);
 
   ClassEntity _findHelperClass(String name) =>
       _findClass(jsHelperLibrary, name);
 
@@ skipping 719 matching lines @@
   ClassEntity get annotationReturnsClass => _findHelperClass('Returns');
 
   ClassEntity get annotationJSNameClass => _findHelperClass('JSName');
 
   FunctionEntity get toStringForNativeObject =>
       _findHelperFunction('toStringForNativeObject');
 
   FunctionEntity get hashCodeForNativeObject =>
       _findHelperFunction('hashCodeForNativeObject');
 }