Move enableNative to target, turn it on by default

pkg/compiler/lib/src/kernel/fasta_support.dart

Index: pkg/compiler/lib/src/kernel/fasta_support.dart
diff --git a/pkg/compiler/lib/src/kernel/fasta_support.dart b/pkg/compiler/lib/src/kernel/fasta_support.dart
index af3b833499166340dc5fbbff5f0f6be69122e314..806d2e848abf4a6031fb8e3d3b69f0001694615d 100644
--- a/pkg/compiler/lib/src/kernel/fasta_support.dart
+++ b/pkg/compiler/lib/src/kernel/fasta_support.dart
@@ -29,6 +29,8 @@ import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 import 'package:front_end/src/fasta/loader.dart' show Loader;
 import 'package:front_end/src/fasta/parser/parser.dart' show optional;
+import 'package:front_end/src/fasta/source/source_library_builder.dart'
+    show SourceLibraryBuilder;
 import 'package:front_end/src/scanner/token.dart' show Token;
 import 'package:front_end/src/fasta/ticker.dart' show Ticker;
 import 'package:front_end/src/fasta/translate_uri.dart' show TranslateUri;
@@ -87,6 +89,10 @@ class KernelTargetForDart2js extends KernelTarget {
             uriToSource);
 
   @override
+  bool enableNative(SourceLibraryBuilder library) =>
+      library.uri.scheme == "dart" || library.isPatch;
+
+  @override
   Token skipNativeClause(Token token) => _skipNative(token);
 
   @override