Massive Attack definitely was the progenitor of trip hop especially in the early nineties when it was relatively unheard of. I think chillwave relies more on spontaneous wandering synths going back and forth while still somehow still sticking to the main beat. Trip hop employs the use of breakbeats a lot more, and while it does use synthesizers sometimes they aren't all over the place. Deadbeat Summer by Neon Indian has a really happy feeling to it, Massive Attack generally has darker sounding stuff and uses more rap but both bands experiment with different moods I guess.
So yeah Massive Attack=trip hop most of the time.
But wow I'm starting to get hooked on Deadbeat Summer, feels like you are a kid taking your first bike ride again on a beautiful day
...........in slow motion