[dart:io] Reland: Adds Platform.localeName

sdk/lib/io/platform.dart

Index: sdk/lib/io/platform.dart
diff --git a/sdk/lib/io/platform.dart b/sdk/lib/io/platform.dart
index b087b053c3203fba77c7cf37c961a5fb0bfb1bae..580ad97db164425a8b4ca4cdcb735273723b31d5 100644
--- a/sdk/lib/io/platform.dart
+++ b/sdk/lib/io/platform.dart
@@ -71,6 +71,7 @@ class Platform {
   static final _operatingSystem = _Platform.operatingSystem;
   static final _localHostname = _Platform.localHostname;
   static final _version = _Platform.version;
+  static final _localeName = _Platform.localeName;
 
   /**
    * Get the number of processors of the machine.
@@ -84,6 +85,11 @@ class Platform {
   static String get pathSeparator => _pathSeparator;
 
   /**
+   * Get the name of the current locale.
+   */
+  static String get localeName => _localeName;
+
+  /**
    * Get a string (`linux`, `macos`, `windows`, `android`, or `ios`)
    * representing the operating system.
    */