Fullscreen button will be disabled if fullscreen is unavailable

[DoomTay]

Description

In the event that fullscreen is unavailable, such as when the player is in an iframe that does not have the allowfullscreen attribute, the fullscreen button will be disabled. This fixes #5290

Specific Changes proposed

fullscreen-toggle.js will check if fullscreen is enabled, and if not, set the button to "disabled"

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[gkatsev]

Sweet, forgot about the disable() helper we had. Even simpler than I imagined!

[wenganxiang]

How to disable a button? I try to add an 'disabled' attribute to any button on control bar, it does not work. On the contrary, it will cause the button not work normally, even I set 'disabled=false'. I use videojs 7