Restrict backend misuse

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 '../common/resolution.dart' show
     Resolution;
 import '../compiler.dart' show
     Compiler;
 import '../core_types.dart' show
     CoreClasses;
 import '../elements/elements.dart' show
     AbstractFieldElement,
     ClassElement,
@@ skipping 653 matching lines @@
     return find(isolateHelperLibrary, '_callInIsolate');
   }
 
   Element get findIndexForNativeSubclassType {
     return findInterceptor('findIndexForNativeSubclassType');
   }
 
   Element get convertRtiToRuntimeType {
     return findHelper('convertRtiToRuntimeType');
   }
+
+  ClassElement get stackTraceClass {
+    return findHelper('_StackTrace');
+  }
+
+  MethodElement _objectNoSuchMethod;
+
+  MethodElement get objectNoSuchMethod {
+    if (_objectNoSuchMethod == null) {
+      _objectNoSuchMethod =
+          coreClasses.objectClass.lookupLocalMember(Identifiers.noSuchMethod_);
+    }
+    return _objectNoSuchMethod;
+  }

[sra1, 2015/11/25 19:02:13]

FYI this can be written

MethodElement get objectNoSuchMethod =>
    _objectNoSuchMethod ??=
        coreClasses.objectClass.lookupLocalMember(Identifiers.noSuchMethod_);

 }