Make textTracks an extern
TextTracks are queried during player initialization whether they're present or not so the method must be present on Player objects. Make sure the method name isn't minified so it's possible to create a Player object without having to extend videojs.Player directly.
Fix capability detection for poster image
We were checking if `backgroundSize` was present on the video element, not the style property of the video element. That meant the IE fallback was being used on all platforms and breaks aspect-ratio preserving poster scaling for those browsers that support it.
Merge pull request #875 from dmlap/hotfix/poster-fallback

Fix capability detection for poster image
Close GH-878: Moved player exports to externs.
Adding line to CHANGELOG
Close GH-887: Fix to reuse HTML5 tech (2). Fixes #884
Adding line to CHANGELOG
Remove added userActivity_ to global
Merge pull request #898 from tuchida/remove-global-userActivity_

Remove added userActivity_ to global