NewUI: Indicate loading when confirmation screen is starting up

[danfinlay]

On stage at EdCon, the New UI confirmation windows took a painful 5 seconds or so to pop up during a live demo.

We should at the very least indicate why it's taking so long (old UI says "estimating gas cost"), and also investigate how we can make it load faster, if it's something we can control.

I wonder if #2991 would improve this performance.

[bdresser]

i weirdly sometimes see a spinner and label that says "generating transaction." probably 1/10 times, can't reproduce reliably. maybe from here?

might be the case that the loader exists just isn't showing properly

[danfinlay]

I just watched a hackathon video where metamask took like 20 seconds for the confirmation window to show anything. It's really painful. At least saying why they're waiting would be a big fix, I think it's often gas estimation.

[whymarrh]

As discussed a few days ago we'll close this for now an break out separate more specific issues