Introduce BackendImpact to separate enqueueing from data.

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

 // Copyright (c) 2014, 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.
 
 part of native;
 
 final RegExp nativeRedirectionRegExp = new RegExp(r'^[a-zA-Z][a-zA-Z_$0-9]*$');
 
 void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
   Compiler compiler = builder.compiler;
   FunctionElement element = builder.work.element;
   NativeEmitter nativeEmitter = builder.nativeEmitter;
   JavaScriptBackend backend = builder.backend;
   DiagnosticReporter reporter = compiler.reporter;
 
   HInstruction convertDartClosure(ParameterElement  parameter,
                                   FunctionType type) {
     HInstruction local = builder.localsHandler.readLocal(parameter);
     ConstantValue arityConstant =
         builder.constantSystem.createInt(type.computeArity());
     HInstruction arity = builder.graph.addConstant(arityConstant, compiler);
     // TODO(ngeoffray): For static methods, we could pass a method with a
     // defined arity.
-    Element helper = backend.getClosureConverter();
+    Element helper = backend.helpers.closureConverter;
     builder.pushInvokeStatic(nativeBody, helper, [local, arity]);
     HInstruction closure = builder.pop();
     return closure;
   }
 
   // Check which pattern this native method follows:
   // 1) foo() native;
   //      hasBody = false
   // 2) foo() native "bar";
   //      No longer supported, this is now done with @JSName('foo') and case 1.
@@ skipping 71 matching lines @@
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeignCode.statement(
         js.js.statementTemplateYielding(
             new js.LiteralStatement(jsCode.dartString.slowToString())),
         <HInstruction>[],
         new SideEffects(),
         null,
         backend.dynamicType));
   }
 }