Work better with Google Docs

[mrmr1993]

This makes <esc> blur out of frames whose body is an editable element.

Fixes #2075.

Notes:

• The focused frame for Google Docs is not what it appears to be: a hidden iframe collects the typing events, but the content is rendered in the main frame.
• I can't find an obvious element that clicking should be enabled for to return focus to the editor, so you have to use the mouse to continue editing.
• Any bindings that use modifier keys will drop focus back into the editor: Docs captures the events for them and uses them to refocus it.

[mrmr1993]

Updated.

[gdh1995]

This new PR breaks my original purpose of preventing the official Vimium from grabbing Esc events on my custom Vimium - my custom Vimium use about:blank as its FindMode iframe. Fortunately, I've dispatched a fake unload event to iframes to force Vimium to exit itself ^_^ , so up to now my custom Vimium is still safe.

[mrmr1993]

I've dispatched a fake unload event to iframes to force Vimium to exit itself

I've been meaning to add a check for event.isTrusted for some time, but I hadn't made a move on it because I couldn't think of a way it would leak data or give privileged access to the page. I'd forgotten that this was a possibility, and this is definitely something pages shouldn't be able to do, as much as the people in #2399 and #2532 might want to.

Thanks for the heads up, I'll throw together a PR now.

[mrmr1993]

I'll throw together a PR now.

Done: #2605.

[philc]

@mrmr1993 this is well-written and well-documented. It solves a valid use case, but adds non-trivial complexity. I'm going to close this due to age and lack of interest.