Bug 1298307 - Check cue's active state first, then verify displaystate. r=alwu,smaug

MozReview-Commit-ID: 4sqPNY9Czsr

--HG--
extra : rebase_source : e612e00520c839c3460d56618b5f3e30e47bc026

dom/media/test/test_webvtt_empty_displaystate.html

@@ -65,11 +65,19 @@ function runTest() {
 
   info("--- add cue ---");
   track.addCue(cue);
-
+  video.ontimeupdate = function () {
+    info("--- video.currentTime is " + video.currentTime);
+  };
   cue.onenter = function () {
     cue.onenter = null;
     isReceivedOnEnterEvent = true;
-    checkCueDisplayState(cue, true /* has display-state */);
+    var cueChrome = SpecialPowers.wrap(cue);
+    info("cueChrome.getActive " + cueChrome.getActive);
+    if (cueChrome.getActive) {
+      checkCueDisplayState(cue, true /* has display-state */);
+    } else {
+      ok(false, "The cue start time is 0, should be always active!?");
+    }
 
     cue.onexit = function () {
       cue.onexit = null;

dom/webidl/VTTCue.webidl

@@ -68,4 +68,6 @@ partial interface VTTCue {
   readonly attribute double computedPosition;
   [ChromeOnly]
   readonly attribute PositionAlignSetting computedPositionAlign;
+  [ChromeOnly]
+  readonly attribute boolean getActive;
 };