To me (BE) this is a very common phrase, describing a trip with lots of short stops. I didn't realise it originally came from the political sphere. (The OED says it comes from train stops where you need to whistle to get the train to stop, and that is is "used attributively to designate a journey with a lot of brief halts; spec. one by a campaigning politician that takes in many undistinguished places in this way. Also fig". But I think the 'undistinguished places' element has been lost over the years. There's nothing undistinguished about the places the Pope visits below!
In its literal sense, someone might say, I'm making a whistlestop tour of cathedral towns in Brittany this weekend. But figuratively, you might also hear, this lecture is going to be a whistlestop tour through 20th century literature.
Transvestites, tapas and twisted statues: a whistlestop tour of south America – in pictures
A new show chronicles the artists, activist and pranksters who have shaped an entire continent
Pope Benedict XVI's whistlestop visit to Britain
The papal tour will take in Edinburgh, Glasgow, London and Birmingham, but the most controversial aspect of the visit is the expense to the state