Synchronous VideoView internal state

[hiroshihorie]

Update VideoView's internal state synchronously so properties such as avSampleBufferDisplayLayer can be accessed immediately.

[hiroshihorie]

If I enforce all properties of VideoView to be accessed from main thread, I can simplify a lot of internal code.
UI components, inheriting from UIView should always be accessed from main thread, so it should be ok.
But I wonder if I make the change, how will it affect current users.

If current users are using VideoView correctly from main thread, nothing will break.