Implement optimized mixin application in dart2js

tests/compiler/dart2js/kernel/compiler_helper.dart

Index: tests/compiler/dart2js/kernel/compiler_helper.dart
diff --git a/tests/compiler/dart2js/kernel/compiler_helper.dart b/tests/compiler/dart2js/kernel/compiler_helper.dart
index 11d9b5d54e2aa31c50d0abaebf9410c4a9ce20f2..cc2219aab6751f6e79dec797dbeb13e5f0129559 100644
--- a/tests/compiler/dart2js/kernel/compiler_helper.dart
+++ b/tests/compiler/dart2js/kernel/compiler_helper.dart
@@ -152,6 +152,13 @@ Future createTemp(Uri entryPoint, Map<String, String> memorySourceFiles,
     });
     entryPoint = dir.uri.resolve(entryPoint.path);
   }
+  return entryPoint;
+}
+
+Future generateDill(Uri entryPoint, Map<String, String> memorySourceFiles,
+    {bool printSteps: false}) async {
+  entryPoint =
+      await createTemp(entryPoint, memorySourceFiles, printSteps: printSteps);
   if (printSteps) {
     print('---- generate dill -----------------------------------------------');
   }
@@ -174,7 +181,7 @@ Future<Compiler> compileWithDill(
     CompilerOutput compilerOutput,
     void beforeRun(Compiler compiler)}) async {
   Uri dillFile =
-      await createTemp(entryPoint, memorySourceFiles, printSteps: printSteps);
+      await generateDill(entryPoint, memorySourceFiles, printSteps: printSteps);
 
   if (printSteps) {
     print('---- compile from dill $dillFile ---------------------------------');