Use memory compiler in compiler_helper.dart.

tests/compiler/dart2js/trust_type_annotations2_test.dart

Index: tests/compiler/dart2js/trust_type_annotations2_test.dart
diff --git a/tests/compiler/dart2js/trust_type_annotations2_test.dart b/tests/compiler/dart2js/trust_type_annotations2_test.dart
index 4eeb0a66366cab14fe21407fd37582d715e7bbc4..f6883805a7b1d069e5f69522d931fd3af45dd390 100644
--- a/tests/compiler/dart2js/trust_type_annotations2_test.dart
+++ b/tests/compiler/dart2js/trust_type_annotations2_test.dart
@@ -30,7 +30,7 @@ main() {
         options: ['--trust-type-annotations']);
     var compiler = result.compiler;
     var element = compiler.mainFunction;
-    var code = compiler.backend.assembleCode(element);
+    var code = compiler.backend.getGeneratedCode(element);
     Expect.isTrue(code.contains('+'), code);
   });
 }