Move remaining helpers to BackendHelpers

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 3fa4a49ec62698d8e200ffd7138b1e773a71c973..9ce01070fa0e514c610fa9726f0e789f2f88a6de 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -73,6 +73,8 @@ import 'enqueue.dart' show
     QueueFilter;
 import 'io/source_information.dart' show
     SourceInformation;
+import 'js_backend/backend_helpers.dart' as js_backend show
+    BackendHelpers;
 import 'js_backend/js_backend.dart' as js_backend show
     JavaScriptBackend;
 import 'library_loader.dart' show
@@ -596,7 +598,7 @@ abstract class Compiler {
       _coreTypes.streamClass = findRequiredElement(library, 'Stream');
     } else if (uri == Uris.dart__native_typed_data) {
       typedDataClass = findRequiredElement(library, 'NativeTypedData');
-    } else if (uri == js_backend.JavaScriptBackend.DART_JS_HELPER) {
+    } else if (uri == js_backend.BackendHelpers.DART_JS_HELPER) {
       patchAnnotationClass = findRequiredElement(library, '_Patch');
       nativeAnnotationClass = findRequiredElement(library, 'Native');
     }