Added code to enable the first caption track if the user has requested captions and one such track …

LayoutTests/media/video-controls-captions-load-by-lang-expected.txt

Index: LayoutTests/media/video-controls-captions-load-by-lang-expected.txt
diff --git a/LayoutTests/media/video-controls-captions-load-by-lang-expected.txt b/LayoutTests/media/video-controls-captions-load-by-lang-expected.txt
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+Tests that appropriate language track is loaded, according to user preferences.
+
+EVENT(canplaythrough)
+
+** Caption button should be visible and enabled because we have a captions track.
+EXPECTED (captionsButtonCoordinates[0] > '0') OK
+EXPECTED (captionsButtonCoordinates[1] > '0') OK
+EXPECTED (captionsButtonElement.disabled == 'false') OK
+
+** The captions track should be listed in textTracks, but disabled. **
+EXPECTED (video.textTracks.length == '2') OK
+EXPECTED (video.textTracks[0].mode == 'disabled') OK
+EXPECTED (video.textTracks[1].mode == 'disabled') OK
+
+** Set the user language preference so that the track will be chosen when the CC button is clicked. **
+RUN(internals.setUserPreferredLanguages(['ar']))
+*** Click the CC button.
+END OF TEST
+