Extract BackendUsage, MirrorsData, and CheckedModeHelpers from Backend.

pkg/compiler/lib/src/js_emitter/full_emitter/nsm_emitter.dart

 // Copyright (c) 2013, 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_emitter.full_emitter.nsm_emitter;
 
 import '../../elements/entities.dart';
 import '../../js/js.dart' as jsAst;
 import '../../js/js.dart' show js;
 import '../../js_backend/js_backend.dart' show GetterName, SetterName;
@@ skipping 55 matching lines @@
           isTrivialNsmHandler(type, argNames, selector, jsName) &&
           reflectionName == null) {
         trivialNsmHandlers.add(selector);
       } else {
         StubMethod method =
             generator.generateStubForNoSuchMethod(jsName, selector);
         addProperty(method.name, method.code);
         if (reflectionName != null) {
           bool accessible = closedWorld.allFunctions
               .filter(selector, null)
-              .any(backend.isMemberAccessibleByReflection);
+              .any(backend.mirrorsData.isMemberAccessibleByReflection);
           addProperty(
               namer.asName('+$reflectionName'), js(accessible ? '2' : '0'));
         }
       }
     }
   }
 
   // Identify the noSuchMethod handlers that are so simple that we can
   // generate them programatically.
   bool isTrivialNsmHandler(
@@ skipping 316 matching lines @@
   }
 
   String get value {
     if (_cachedValue == null) {
       _cachedValue = _computeDiffEncoding();
     }
 
     return _cachedValue;
   }
 }