Make JavaScriptBackend.processAnnotations element-model agnostic

tests/compiler/dart2js/expect_annotations_test.dart

Index: tests/compiler/dart2js/expect_annotations_test.dart
diff --git a/tests/compiler/dart2js/expect_annotations_test.dart b/tests/compiler/dart2js/expect_annotations_test.dart
index 9ca88103b18316301eda3c31450b62bff38c2617..136cb52a7c79e45aa2b2cdcad990dbac4a4caea8 100644
--- a/tests/compiler/dart2js/expect_annotations_test.dart
+++ b/tests/compiler/dart2js/expect_annotations_test.dart
@@ -84,7 +84,7 @@ main() {
         TypeMask expectedReturnType: null,
         bool expectAssumeDynamic: false}) {
       LibraryElement mainApp = compiler.mainApp;
-      Element method = mainApp.find(name);
+      MethodElement method = mainApp.find(name);
       Expect.isNotNull(method);
       Expect.equals(expectNoInline, backend.annotations.noInline(method),
           "Unexpected annotation of @NoInline on '$method'.");