That's one of the great political cliches. It is said to have been coined by an Associated Press reporter who covered the 1920 Republican National Convention in Chicago.
Theodore Roosevelt had been considered the early front-runner for the Republicans' 1920 presidential nomination, but he died in 1919. When the convention began, it was a wide-open race. General Leonard Wood led on the first four ballots. He was a career army man, who at one point had been Army Chief of Staff. He was neck-and-neck with Illinois Governor Frank Lowden through the eighth ballot. Meanwhile, Senator Warren Harding of Ohio made slow but steady gains from the third ballot onward.
Party power brokers met in the Blackstone Hotel in Chicago. The room in which they met at that hotel is the original smoke-filled room. There, they decided that none of the better-known candidates had a chance to put together majority support among the delegates, so they compromised on Harding, who then won the nomination on the 10th ballot.
I looked on the 2008 Republican convention website, but couldn't find any mention of smoking policy. But my guess is that smoking will be banned in any meeting room of either party's convention. If so, you won't find a smoke-filled room, literally speaking, at either convention. But more to the point, you won't find a meeting of power brokers to resolve a convention deadlock. Both nominations were decided by the primaries and caucuses that both parties held between January and June of this year. The conventions will ratify those choices, but the outcome has already been decided.
By the way, Harding won that election but, as I wrote here, all did not go well.