Support text track selection in video controls

third_party/WebKit/LayoutTests/media/video-controls-captions-expected.txt

-Tests that the closed captions button, when toggled, updates the text track display area.
+Tests that the closed captions button enables track switching
 
 EVENT(canplaythrough)
 
 ** Caption button should be visible and enabled.
 EXPECTED (captionsButtonCoordinates[0] > '0') OK
 EXPECTED (captionsButtonCoordinates[1] > '0') OK
 EXPECTED (captionsButtonElement.disabled == 'false') OK
 
 ** The captions track should be listed in textTracks, but not yet loaded. **
 EXPECTED (video.textTracks.length == '1') OK
 EXPECTED (video.textTracks[0].mode == 'disabled') OK
 Failed to find text track container element
 
-** Captions track should load and captions should become visible after button is clicked **
+** Captions track should load and captions should become visible after a track is selected **
 *** Click the CC button.
 EXPECTED (textTrackDisplayElement(video, 'display').innerText == 'Lorem') OK
 
-** Captions should not be visible after button is clicked again **
+** Captions should not be visible after Off is clicked **
 *** Click the CC button.
 No text track cue with display id '-webkit-media-text-track-display' is currently visible
 
 ** Remove DOM node representing the track element **
 
 ** Caption button should not be visible.
 EXPECTED (captionsButtonCoordinates[0] <= '0') OK
 EXPECTED (captionsButtonCoordinates[1] <= '0') OK
 
 ** Add non-default text track through HTML with unloadable URI **
@@ skipping 14 matching lines @@
 EXPECTED (captionsButtonCoordinates[1] <= '0') OK
 
 ** Add a text track through JS to the video element **
 
 ** Caption button should be visible and enabled.
 EXPECTED (captionsButtonCoordinates[0] > '0') OK
 EXPECTED (captionsButtonCoordinates[1] > '0') OK
 EXPECTED (captionsButtonElement.disabled == 'false') OK
 END OF TEST