Try better webview focus tracking solution in Electron 6+

[mjbvz]

From #64729

Tracks revisiting how we track focus of webviews. The focus apis are broken in Electron 3 and as a workaround, we use polling to determine when the webview contents have become focused. This is not a good solution and we should revisit it with Electron 4 to see if the focus apis have been fixed

[bpasero]

Our electron-4.0.x branch is up to date and running with Electron 4.0.1

[mjbvz]

Seems the issue is still in 4.0 in my testing. Here's the electron issue currently tracking this: electron/electron#15718. I'll also test in the exploration builds just to confirm it hasn't been fixed yet, so pushing this to July

iframe based webviews do not seem to suffer from this issue

[bpasero]

Ok, updating labels.