Stop resolving all of js_helper unconditionally.

sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart

 // Copyright (c) 2012, 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 js_backend;
 
 class ConstantEmitter  {
   ConstantReferenceEmitter _referenceEmitter;
   ConstantInitializerEmitter _initializerEmitter;
 
@@ skipping 276 matching lines @@
         (constant.protoValue != null && emittedArgumentCount != 4)) {
       badFieldCountError();
     }
 
     return new jsAst.New(
         new jsAst.VariableUse(getJsConstructor(classElement)),
         arguments);
   }
 
   jsAst.Expression visitType(TypeConstant constant) {
-    SourceString helperSourceName = const SourceString('createRuntimeType');
-    Element helper = compiler.findHelper(helperSourceName);
     JavaScriptBackend backend = compiler.backend;
+    Element helper = backend.getCreateRuntimeType();
     String helperName = backend.namer.getName(helper);
     DartType type = constant.representedType;
     Element element = type.element;
     String name = backend.rti.getRawTypeRepresentation(type);
     jsAst.Expression typeName = new jsAst.LiteralString("'$name'");
     return new jsAst.Call(
         new jsAst.PropertyAccess.field(
             new jsAst.VariableUse(namer.CURRENT_ISOLATE),
             helperName),
         [typeName]);
   }
 
   jsAst.Expression visitConstructed(ConstructedConstant constant) {
     return new jsAst.New(
         new jsAst.VariableUse(getJsConstructor(constant.type.element)),
         _array(constant.fields));
   }
 
   List<jsAst.Expression> _array(List<Constant> values) {
     List<jsAst.Expression> valueList = <jsAst.Expression>[];
     for (int i = 0; i < values.length; i++) {
       valueList.add(_reference(values[i]));
     }
     return valueList;
   }
 }