This is turning into a interesting match as now the WI are in full control and its there match to win as SL won't be able to chase down 377. I thought the WI have played well to at least try and get a win here by declaring early on and making SL bat late on day 4, now SL will need to survive the whole day on a day 5 pitch. It will be an exciting end to the match, its a shame that its not on T.V here but I'll see if I can watch it on a stream.
IMO, West Indies delayed the declaration by some 10 overs and it may prove costly to them. On the 4th day, the West Indies bowlers got just 9 overs against the Sri Lankan batsmen. If they got some 15-20 overs, then in all probability they could have at least taken a couple of wickets and the game would have been in their control. In particular, Kraigg Brathwaite was very slow in scoring the runs. They had enough wickets in hand, so it makes no sense to bat in such a slow manner.
Not sure if the 10 overs would of helped as SL were able to bat the whole day and only lost 2 wickets. We don't know for sure as anything could of happened in them 10 overs but going by how SL were able to bat out a full day shows that it might of still ended in a draw or even a SL win. We got a fair idea that this would be a draw after the end of day 2, it seemed that both teams were playing for the draw at different stages of the match and even though the WI did declare as you said they batted for too long.