Fix regression caused by r178354 where options in optgroup not indented

Source/core/css/html.css

Index: Source/core/css/html.css
diff --git a/Source/core/css/html.css b/Source/core/css/html.css
index 6566aff360bd29c489fc63ee2551a1a05316ff37..c49329f100bb99bc8bf09dc2ebb9180fb0ef142f 100644
--- a/Source/core/css/html.css
+++ b/Source/core/css/html.css
@@ -791,6 +791,10 @@ option {
     min-height: 1.2em;
 }
 
+select:-internal-list-box optgroup option:before {
+    content: "\00a0\00a0\00a0\00a0";;
+}
+
 select:-internal-list-box option,
 select:-internal-list-box optgroup {
     line-height: initial !important;