Revert "Reduce use of Element in optimize.dart"

pkg/compiler/lib/src/common/backend_api.dart

Index: pkg/compiler/lib/src/common/backend_api.dart
diff --git a/pkg/compiler/lib/src/common/backend_api.dart b/pkg/compiler/lib/src/common/backend_api.dart
index d05b8448a82ecce2a8c886f93768878a87a69c9e..4fba499e66ad93580a1727d2a82b873aa282e379 100644
--- a/pkg/compiler/lib/src/common/backend_api.dart
+++ b/pkg/compiler/lib/src/common/backend_api.dart
@@ -419,6 +419,5 @@ abstract class BackendClasses {
 
   bool isDefaultEqualityImplementation(Element element);
   bool isInterceptorClass(ClassElement cls);
-  bool isNativeClass(ClassElement element);
-  bool isNativeMember(MemberElement element);
+  bool isNative(Element element);
 }