Move remaining helpers to BackendHelpers

pkg/compiler/lib/src/js_backend/js_interop_analysis.dart

Index: pkg/compiler/lib/src/js_backend/js_interop_analysis.dart
diff --git a/pkg/compiler/lib/src/js_backend/js_interop_analysis.dart b/pkg/compiler/lib/src/js_backend/js_interop_analysis.dart
index e5c9b2543ea77f17e49255888113f95b769cd977..15916f90251c72b06ad98013aa606395eb009d3c 100644
--- a/pkg/compiler/lib/src/js_backend/js_interop_analysis.dart
+++ b/pkg/compiler/lib/src/js_backend/js_interop_analysis.dart
@@ -30,6 +30,7 @@ import '../js/js.dart' show js;
 import '../universe/selector.dart' show Selector;
 import '../universe/universe.dart' show SelectorConstraints;
 
+import 'backend_helpers.dart' show BackendHelpers;
 import 'js_backend.dart' show JavaScriptBackend;
 
 class JsInteropAnalysis {
@@ -44,11 +45,13 @@ class JsInteropAnalysis {
 
   JsInteropAnalysis(this.backend);
 
+  BackendHelpers get helpers => backend.helpers;
+
   void onQueueClosed() {
     if (_inCodegen) return;
 
-    if (backend.jsAnnotationClass != null) {
-      nameField = backend.jsAnnotationClass.lookupMember('name');
+    if (helpers.jsAnnotationClass != null) {
+      nameField = helpers.jsAnnotationClass.lookupMember('name');
       backend.compiler.libraryLoader.libraries
           .forEach(processJsInteropAnnotationsInLibrary);
     }
@@ -64,7 +67,7 @@ class JsInteropAnalysis {
           annotation.constant);
       if (constant == null || constant is! ConstructedConstantValue) continue;
       ConstructedConstantValue constructedConstant = constant;
-      if (constructedConstant.type.element == backend.jsAnnotationClass) {
+      if (constructedConstant.type.element == helpers.jsAnnotationClass) {
         ConstantValue value = constructedConstant.fields[nameField];
         if (value.isString) {
           StringConstantValue stringValue = value;
@@ -89,7 +92,7 @@ class JsInteropAnalysis {
       ClassElement classElement = element;
 
       if (!classElement
-          .implementsInterface(backend.jsJavaScriptObjectClass)) {
+          .implementsInterface(helpers.jsJavaScriptObjectClass)) {
         backend.reporter.reportErrorMessage(classElement,
             MessageKind.JS_INTEROP_CLASS_CANNOT_EXTEND_DART_CLASS, {
           'cls': classElement.name,