Support the 'lrm', 'rlm' and 'nbsp' entities in the WebVTTTokenizer

LayoutTests/media/track/captions-webvtt/tc022-entities.vtt

Index: LayoutTests/media/track/captions-webvtt/tc022-entities.vtt
diff --git a/LayoutTests/media/track/captions-webvtt/tc022-entities.vtt b/LayoutTests/media/track/captions-webvtt/tc022-entities.vtt
index 79558e570c9f867c2357f71e08b864c5411c5b84..bed93395eaa92fa1cf1dc226cef93fe87eed0837 100644
--- a/LayoutTests/media/track/captions-webvtt/tc022-entities.vtt
+++ b/LayoutTests/media/track/captions-webvtt/tc022-entities.vtt
@@ -1,5 +1,5 @@
 WEBVTT
-Cue content with escape characters for &, <, and >.
+Cue content with escape characters for &, <, >, LRM, RLM and non-breaking space.
 
 1
 00:00:00.000 --> 00:00:30.500 align:start position:20%
@@ -12,3 +12,15 @@ This cue has a less than &lt; character.
 3
 00:01:01.000 --> 00:02:00.500 align:start position:20%
 This cue has a greater than &gt; character.
+
+4
+00:02:01.000 --> 00:02:30.500 align:start position:20%
+This cue has a Left-to-Right Mark &lrm;.
+
+5
+00:02:31.000 --> 00:03:00.500 align:start position:20%
+This cue has a Right-to-Left Mark &rlm;.
+
+6
+00:03:01.000 --> 00:03:30.500 align:start position:20%
+This cue has a non-breaking space &nbsp;.