Bug 1328966 - Accept \r as a valid line ending. r=alwu

See https://w3c.github.io/webvtt/#webvtt-line-terminator for
allowed values.

MozReview-Commit-ID: C62Lu4PNQRE

--HG--
extra : rebase_source : 7c9215477ad39dbe319374357ef8f19d96ed423c

dom/media/webvtt/vtt.jsm

@@ -1438,7 +1438,7 @@ this.EXPORTED_SYMBOLS = ["WebVTT"];
           if (!line) {
             // Since the data receiving is async, we need to wait until the
             // buffer gets the full line.
-            if (!/\r\n|\n/.test(self.buffer)) {
+            if (!/\r\n|\n|\r/.test(self.buffer)) {
               return this;
             }
             line = collectNextLine();