Extract BackendUsage, MirrorsData, and CheckedModeHelpers from Backend.

pkg/compiler/lib/src/js_emitter/metadata_collector.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.metadata_collector;
 
 import 'package:js_ast/src/precedence.dart' as js_precedence;
 
 import '../common.dart';
 import '../compiler.dart' show Compiler;
@@ skipping 146 matching lines @@
 
   MetadataCollector(this._compiler, this._emitter) {
     _globalMetadataMap = new Map<String, _BoundMetadataEntry>();
   }
 
   JavaScriptBackend get _backend => _compiler.backend;
   TypeVariableHandler get _typeVariableHandler => _backend.typeVariableHandler;
   DiagnosticReporter get reporter => _compiler.reporter;
 
   bool _mustEmitMetadataFor(Element element) {
-    return _backend.mustRetainMetadata &&
-        _backend.referencedFromMirrorSystem(element);
+    return _backend.mirrorsData.mustRetainMetadata &&
+        _backend.mirrorsData.referencedFromMirrorSystem(element);
   }
 
   /// The metadata function returns the metadata associated with
   /// [element] in generated code.  The metadata needs to be wrapped
   /// in a function as it refers to constants that may not have been
   /// constructed yet.  For example, a class is allowed to be
   /// annotated with itself.  The metadata function is used by
   /// mirrors_patch to implement DeclarationMirror.metadata.
   jsAst.Fun buildMetadataFunction(Element element) {
     if (!_mustEmitMetadataFor(element)) return null;
@@ skipping 138 matching lines @@
     });
   }
 
   jsAst.Expression _computeTypeRepresentation(ResolutionDartType type,
       {ignoreTypeVariables: false}) {
     jsAst.Expression representation =
         _backend.rtiEncoder.getTypeRepresentation(type, (variable) {
       if (ignoreTypeVariables) return new jsAst.LiteralNull();
       return _typeVariableHandler.reifyTypeVariable(variable.element);
     }, (ResolutionTypedefType typedef) {
-      return _backend.isAccessibleByReflection(typedef.element);
+      return _backend.mirrorsData.isAccessibleByReflection(typedef.element);
     });
 
     if (representation is jsAst.LiteralString) {
       // We don't want the representation to be a string, since we use
       // strings as indicator for non-initialized types in the lazy emitter.
       reporter.internalError(
           NO_LOCATION_SPANNABLE, 'reified types should not be strings.');
     }
 
     return representation;
@@ skipping 88 matching lines @@
     if (token is _ForwardingMetadataEntry && !token.isBound) {
       _foundUnboundToken = true;
     }
   }
 
   bool findUnboundPlaceholders(jsAst.Node node) {
     node.accept(this);
     return _foundUnboundToken;
   }
 }