[dart:io] Adds Platform.ansiSupported

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 75f7ffd0e46b49bc7e0d9cbe574af6ce8f5d8c2e..242f6bbc2d969ff717cb36c494238bb0b3a20b67 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 _ansiSupported = _Platform.ansiSupported;
 
   /**
    * Get the number of processors of the machine.
@@ -124,6 +125,14 @@ class Platform {
    */
    static final bool isFuchsia = (_operatingSystem == "fuchsia");
 
+   /**
+    * When stdio is connected to a terminal, whether ANSI codes are supported.
+    *
+    * This value is hard-coded to `true`, except on Windows where only more
+    * recent versions of Windows 10 support the codes.
+    */
+   static final bool ansiSupported = _ansiSupported;
+
   /**
    * Get the environment for this process.
    *