Extract BackendUsage, MirrorsData, and CheckedModeHelpers from Backend.

pkg/compiler/lib/src/deferred_load.dart

 // Copyright (c) 2014, 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 deferred_load;
 
 import 'common/tasks.dart' show CompilerTask;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart' show ConstantExpression;
@@ skipping 547 matching lines @@
   /// The elements are added with [_mapDependencies].
   void _addMirrorElements() {
     void mapDependenciesIfResolved(
         Element element, _DeferredImport deferredImport) {
       // If an element is the target of a MirrorsUsed annotation but never used
       // It will not be resolved, and we should not call isNeededForReflection.
       // TODO(sigurdm): Unresolved elements should just answer false when
       // asked isNeededForReflection. Instead an internal error is triggered.
       // So we have to filter them out here.
       if (element is AnalyzableElementX && !element.hasTreeElements) return;
-      if (compiler.backend.isAccessibleByReflection(element)) {
+      if (compiler.backend.mirrorsData.isAccessibleByReflection(element)) {
         _mapDependencies(
             element: element, import: deferredImport, isMirrorUsage: true);
       }
     }
 
     // For each deferred import we analyze all elements reachable from the
     // imported library through non-deferred imports.
     void handleLibrary(LibraryElement library, _DeferredImport deferredImport) {
       library.implementation.forEachLocalMember((Element element) {
         mapDependenciesIfResolved(element, deferredImport);
@@ skipping 472 matching lines @@
 
   bool operator ==(other) {
     if (other is! _DeclaredDeferredImport) return false;
     return declaration == other.declaration;
   }
 
   int get hashCode => declaration.hashCode * 17;
 
   String toString() => '$declaration';
 }