Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/native/behavior.dart

Index: pkg/compiler/lib/src/native/behavior.dart
diff --git a/pkg/compiler/lib/src/native/behavior.dart b/pkg/compiler/lib/src/native/behavior.dart
index 106fbeafeb29d83e1fe390fe5133f0b6eaa50288..936c8c7dd10f6d7f5b0a9f22b0fbd858682a89d4 100644
--- a/pkg/compiler/lib/src/native/behavior.dart
+++ b/pkg/compiler/lib/src/native/behavior.dart
@@ -15,8 +15,6 @@ import '../elements/entities.dart';
 import '../elements/resolution_types.dart';
 import '../elements/types.dart';
 import '../js/js.dart' as js;
-import '../js_backend/js_backend.dart';
-import '../js_backend/backend_helpers.dart';
 import '../tree/tree.dart';
 import '../universe/side_effects.dart' show SideEffects;
 import '../util/util.dart';
@@ -849,7 +847,6 @@ class NativeBehavior {
 abstract class BehaviorBuilder {
   CommonElements get commonElements;
   BackendClasses get backendClasses;
-  BackendHelpers get helpers;
   DiagnosticReporter get reporter;
   ConstantEnvironment get constants;
   bool get trustJSInteropTypeAnnotations;
@@ -863,9 +860,9 @@ abstract class BehaviorBuilder {
     if (metadata.isEmpty) return;
 
     List creates =
-        _collect(metadata, helpers.annotationCreatesClass, lookupType);
+        _collect(metadata, commonElements.annotationCreatesClass, lookupType);
     List returns =
-        _collect(metadata, helpers.annotationReturnsClass, lookupType);
+        _collect(metadata, commonElements.annotationReturnsClass, lookupType);
 
     if (creates != null) {
       _behavior.typesInstantiated
@@ -965,7 +962,7 @@ abstract class BehaviorBuilder {
           // annotations. This means that to some degree we still use the return
           // type to decide whether to include native types, even if we don't
           // trust the type annotation.
-          ClassElement cls = helpers.jsJavaScriptObjectClass;
+          ClassElement cls = commonElements.jsJavaScriptObjectClass;
           cls.ensureResolved(resolution);
           _behavior.typesInstantiated.add(cls.thisType);
         } else {
@@ -1055,12 +1052,6 @@ class ResolverBehaviorBuilder extends BehaviorBuilder {
   DiagnosticReporter get reporter => compiler.reporter;
 
   @override
-  BackendHelpers get helpers {
-    JavaScriptBackend backend = compiler.backend;
-    return backend.helpers;
-  }
-
-  @override
   BackendClasses get backendClasses => compiler.backend.backendClasses;
 
   @override