Stop working around issue 7781 in Pub.

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index 665680e828ebc871f4c4cec1e81cc2a4fd8680ac..18475eafb220fa8925d07987c34ab8a89a9b6f74 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -189,10 +189,10 @@ Future<Directory> ensureDir(path) {
 
     return ensureDir(dirname(path)).then((_) {
       return createDir(path).catchError((asyncError) {
-        var error = getRealError(asyncError);
-        if (error is! DirectoryIOException) throw asyncError;
+        if (asyncError.error is! DirectoryIOException) throw asyncError;
         // Error 17 means the directory already exists (or 183 on Windows).
-        if (error.osError.errorCode == 17 || error.osError.errorCode == 183) {
+        if (asyncError.error.osError.errorCode == 17 ||
+            asyncError.error.osError.errorCode == 183) {
           log.fine("Got 'already exists' error when creating directory.");
           return _getDirectory(path);
         }