Fix for webviews using default (empty) BeginFrameSubscription implementation

[brenca]

This PR adds a small patch to fix electron/electron#5665
RenderWidgetHostViewChildFrame was missing some functions, I tried to keep the implementation as small as possible for easier maintenance.

[IsaiahJTurner]

@brenca I think something happened with copy and pasting source changes.

[brenca]

@IsaiahJTurner What do you mean?

[IsaiahJTurner]

Take that back. I hadn't seen a .patch before. I'll test it shortly, thanks for doing this!

[brenca]

:) It was actually an issue with chromium's code, this is why I made a patch file to fix it. Also, you might want to wait until @zcbenz pulls this in (if he will :) ) and it gets included in the next electron release, since building a custom libchromiumcontent can easily take a full day (and most of it is just the building!), if you don't have machine specifically made for this kind of stuff. I couldn't test this out on Mac, but I did test it on Windows (the screenshot I added) and the subscription seems to be working perfectly now.

[zeke]

💰

[gerhardberger]

I tried it out on macOS and works like a charm! 👌

[zcbenz]

👍