fix: Fix getVideoPlaybackQuality in WebOS 3 (#4316)
fix: Fix getVideoPlaybackQuality in WebOS 3 (#4316)

It seems that webkitDroppedFrameCount is not included in the prototype but it is included in the video element itself, that's why it fails in WebOS 3.

Closes https://github.com/shaka-project/shaka-player/issues/4313
shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player