[dart:io] Reland: Adds Platform.localeName

sdk/lib/_internal/js_runtime/lib/io_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/io_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/io_patch.dart b/sdk/lib/_internal/js_runtime/lib/io_patch.dart
index 46f8404ab2d636e415774b8926770b43467225d4..e7ed5bef5c6f5f5f6c1b6c8a63e64745b1a69c0b 100644
--- a/sdk/lib/_internal/js_runtime/lib/io_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/io_patch.dart
@@ -250,6 +250,11 @@ class _Platform {
   static String _version() {
     throw new UnsupportedError("Platform._version");
   }
+
+  @patch
+  static String _localeName() {
+    throw new UnsupportedError("Platform._localeName");
+  }
 }
 
 @patch