Extract BackendUsage, MirrorsData, and CheckedModeHelpers from Backend.

pkg/compiler/lib/src/js_emitter/native_generator.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 dart2js.js_emitter.native_generator;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
 import '../js_backend/js_backend.dart' show JavaScriptBackend;
 
 import 'model.dart';
 
 class NativeGenerator {
   static bool needsIsolateAffinityTagInitialization(JavaScriptBackend backend) {
-    return backend.needToInitializeIsolateAffinityTag;
+    return backend.backendUsage.needToInitializeIsolateAffinityTag;
   }
 
   /// Generates the code for isolate affinity tags.
   ///
   /// Independently Dart programs on the same page must not interfer and
   /// this code sets up the variables needed to guarantee that behavior.
   static jsAst.Statement generateIsolateAffinityTagInitialization(
       JavaScriptBackend backend,
       jsAst.Expression generateEmbeddedGlobalAccess(String global),
       jsAst.Expression internStringFunction) {
-    assert(backend.needToInitializeIsolateAffinityTag);
+    assert(backend.backendUsage.needToInitializeIsolateAffinityTag);
 
     jsAst.Expression getIsolateTagAccess =
         generateEmbeddedGlobalAccess(embeddedNames.GET_ISOLATE_TAG);
     jsAst.Expression isolateTagAccess =
         generateEmbeddedGlobalAccess(embeddedNames.ISOLATE_TAG);
     jsAst.Expression dispatchPropertyNameAccess =
         generateEmbeddedGlobalAccess(embeddedNames.DISPATCH_PROPERTY_NAME);
 
     return js.statement(
         '''
@@ skipping 20 matching lines @@
             break;
           }
         }
         if (#initializeDispatchProperty) {
           #dispatchPropertyName = #getIsolateTag("dispatch_record");
         }
       }();
     ''',
         {
           'initializeDispatchProperty':
-              backend.needToInitializeDispatchProperty,
+              backend.backendUsage.needToInitializeDispatchProperty,
           'internStringFunction': internStringFunction,
           'getIsolateTag': getIsolateTagAccess,
           'isolateTag': isolateTagAccess,
           'dispatchPropertyName': dispatchPropertyNameAccess
         });
   }
 
   static String generateIsolateTagRoot() {
     // TODO(sra): MD5 of contributing source code or URIs?
     return 'ZxYxX';
@@ skipping 129 matching lines @@
           'info': infoAccess,
           'constructor': constructorAccess,
           'subclassRead': subclassRead,
           'interceptorsByTagAccess': interceptorsByTagAccess,
           'leafTagsAccess': leafTagsAccess,
           'nativeSuperclassTagName': embeddedNames.NATIVE_SUPERCLASS_TAG_NAME,
           'allowNativesSubclassing': true
         });
   }
 }