Video focus does not switch in Chrome and Safari when clicking play, pause, or seeking

[alexsielicki]

This is the same problem I found in VideoSwarm. Chrome and Safari do not fire the click even when the user clicks on the video element's play or pause buttons or seeks the video. Fix is the same too, add code that switches video focus to each video's pause, play, and seeked event handlers.

[alexsielicki]

I tested this again after rewriting a lot of the event handling due to #780. Here is the current status:

• In Chrome 62 on macOS, focus does not switch when playing, pausing, or seeking video.
• In Safari 11 on macOS, focus does switch with play, pause, and seek, so everything works as expected.
• In Firefox 52 on macOS, focus does switch but the controls need to clicked again to play, pause, or seek if the frame didn't have focus initially.

We should standardize this so it works like in Safari 11, meaning that clicking a control in an unfocused frame both triggers the control and brings focus to the frame.