Enable enums by default.

pkg/compiler/lib/src/dart2js.dart

Index: pkg/compiler/lib/src/dart2js.dart
diff --git a/pkg/compiler/lib/src/dart2js.dart b/pkg/compiler/lib/src/dart2js.dart
index fc3b766216fcfa50d1dad9ac77a1ee8c0e73dedd..d0e9a5b8a19e66bcd140f485c23c3da93454ae07 100644
--- a/pkg/compiler/lib/src/dart2js.dart
+++ b/pkg/compiler/lib/src/dart2js.dart
@@ -341,7 +341,12 @@ Future<api.CompilationResult> compile(List<String> argv) {
     new OptionHandler('--csp', passThrough),
     new OptionHandler('--enable-experimental-mirrors', passThrough),
     new OptionHandler('--enable-async', setEnableAsync),
-    new OptionHandler('--enable-enum', passThrough),
+    new OptionHandler('--enable-enum', (_) {
+      diagnosticHandler.info(
+          "Option '--enable-enum' is no longer needed. "
+          "Enums are supported by default.",
+          api.Diagnostic.HINT);
+    }),
     new OptionHandler('--allow-native-extensions', setAllowNativeExtensions),
     new OptionHandler('--generate-code-with-compile-time-errors', passThrough),