You can't copyright game mechanics. So, if you replace the sprites with legally distinct ones and write the code yourself, there are no laws broken.

It looks like the game is part of Chrome but not Chromium, so it would be under Google's copyright. So if you mean a copy using the same assets then no. If you mean can you create an endless runner featuring a dinosaur, yes

Pretty sure the answer is: Yes, since I believe it's part of the open source project chromium, it would be under the same open source license.

This already exists

Probably legal unless you use their art.

Could they sue the hell out of you, block the game on app/play store and generally make your life miserable if they felt like it even if it would not hold up in a court: Yep.