Couple of backend fixes:

sdk/lib/_internal/compiler/implementation/js_backend/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;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 567 matching lines @@
         }
         diffEncoding.write(short);
       }
       nameCounter++;
     }
 
     // Startup code that loops over the method names and puts handlers on the
     // Object class to catch noSuchMethod invocations.
     ClassElement objectClass = compiler.objectClass;
     String createInvocationMirror = namer.getName(
-        compiler.createInvocationMirrorElement);
+        backend.getCreateInvocationMirror());
     String noSuchMethodName = namer.publicInstanceMethodNameByArity(
         Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);
     var type = 0;
     if (useDiffEncoding) {
       statements.addAll([
         js('var objectClassObject = '
            '        collectedClasses["${namer.getName(objectClass)}"],'
            '    shortNames = "$diffEncoding".split(","),'
            '    nameNumber = 0,'
            '    diffEncodedString = shortNames[0],'
@@ skipping 2220 matching lines @@
     return type == 0;
   }
 
   void emitNoSuchMethodHandlers(DefineStubFunction defineStub) {
     // Do not generate no such method handlers if there is no class.
     if (compiler.codegenWorld.instantiatedClasses.isEmpty) return;
 
     String noSuchMethodName = namer.publicInstanceMethodNameByArity(
         Compiler.NO_SUCH_METHOD, Compiler.NO_SUCH_METHOD_ARG_COUNT);
 
-    Element createInvocationMirrorElement =
-        compiler.findHelper(const SourceString("createInvocationMirror"));
+    Element createInvocationMirrorElement = backend.getCreateInvocationMirror();
     String createInvocationMirrorName =
         namer.getName(createInvocationMirrorElement);
 
     // Keep track of the JavaScript names we've already added so we
     // do not introduce duplicates (bad for code size).
     Map<String, Selector> addedJsNames = new Map<String, Selector>();
 
     void addNoSuchMethodHandlers(SourceString ignore, Set<Selector> selectors) {
       // Cache the object class and type.
       ClassElement objectClass = compiler.objectClass;
@@ skipping 40 matching lines @@
 
       String methodName = selector.invocationMirrorMemberName;
       String internalName = namer.invocationMirrorInternalName(selector);
       if (!haveVeryFewNoSuchMemberHandlers &&
           isTrivialNsmHandler(type, argNames, selector, internalName)) {
         trivialNsmHandlers.add(selector);
         return null;
       }
 
       String createInvocationMirror = namer.getName(
-          compiler.createInvocationMirrorElement);
+          backend.getCreateInvocationMirror());
 
       assert(backend.isInterceptedName(Compiler.NO_SUCH_METHOD));
       jsAst.Expression expression = js('this.$noSuchMethodName')(
           [js('this'),
            js(namer.CURRENT_ISOLATE)[createInvocationMirror]([
                js.string(compiler.enableMinification ?
                          internalName : methodName),
                js.string(internalName),
                type,
                new jsAst.ArrayInitializer.from(
@@ skipping 1260 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;