Work around flaky TextTrackList tests that will be stable with Oilpan

LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html

Index: LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html
diff --git a/LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html b/LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html
index 70f3ed1607bf31b3f20cf3b39dffeefeddbc670e..922bf780157eceb1d038aa5f68a63e02dbe33232 100644
--- a/LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html
+++ b/LayoutTests/media/track/opera/interfaces/TextTrackList/onremovetrack.html
@@ -5,7 +5,10 @@
 <div id=log></div>
 <script>
 setup(function(){
-    window.tracks = document.createElement('video').textTracks;
+    // TODO(philipj): Remove this test in favor of those in web-platform-tests
+    // once Oilpan has shipped. https://crbug.com/503852
+    window.video = document.createElement('video');
+    window.tracks = video.textTracks;
     window.ev = new Event('removetrack');
     window.ran = false;
     window.cb = function() { ran = true; };