Move remaining helpers to BackendHelpers

pkg/compiler/lib/src/js_backend/backend_impact.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_helpers.impact;
 
 import '../common/names.dart' show
     Identifiers;
 import '../compiler.dart' show
     Compiler;
@@ skipping 121 matching lines @@
         needsInt(
             'Needed to encode the invocation kind of super.noSuchMethod.'),
         needsList(
             'Needed to encode the arguments of super.noSuchMethod.'),
         needsString(
             'Needed to encode the name of super.noSuchMethod.')]);
 
   BackendImpact get constantMapLiteral {
 
     ClassElement find(String name) {
-      return helpers.find(backend.jsHelperLibrary, name);
+      return helpers.find(helpers.jsHelperLibrary, name);
     }
 
     return new BackendImpact(
       instantiatedClasses: [
         find(JavaScriptMapConstant.DART_CLASS),
         find(JavaScriptMapConstant.DART_PROTO_CLASS),
         find(JavaScriptMapConstant.DART_STRING_CLASS),
         find(JavaScriptMapConstant.DART_GENERAL_CLASS)]);
   }
 
@@ skipping 46 matching lines @@
         helpers.streamIteratorConstructor]);
 
   BackendImpact get stringInterpolation => new BackendImpact(
       staticUses: [
         helpers.stringInterpolationHelper]);
 
   BackendImpact get catchStatement => new BackendImpact(
       staticUses: [
         helpers.exceptionUnwrapper],
       instantiatedClasses: [
-        backend.jsPlainJavaScriptObjectClass,
-        backend.jsUnknownJavaScriptObjectClass]);
+        helpers.jsPlainJavaScriptObjectClass,
+        helpers.jsUnknownJavaScriptObjectClass]);
 
   BackendImpact get throwExpression => new BackendImpact(
       // We don't know ahead of time whether we will need the throw in a
       // statement context or an expression context, so we register both
       // here, even though we may not need the throwExpression helper.
       staticUses: [
         helpers.wrapExceptionHelper,
         helpers.throwExpressionHelper]);
 
   BackendImpact get lazyField => new BackendImpact(
@@ skipping 73 matching lines @@
       staticUses: [
         // We will neeed to add the "$is" and "$as" properties on the
         // JavaScript object prototype, so we make sure
         // [:defineProperty:] is compiled.
         helpers.defineProperty]);
 
   BackendImpact get closure => new BackendImpact(
       instantiatedClasses: [
         coreClasses.functionClass]);
 }