[A_Brandybuck]

Maybe it is far-fetched, but Gandalf (or rather his former person Olórin) is a specialist for giving visions to the Elves. The passage in the Sil tells us that, but it doesn't really fit the dream of Boromir and Faramir. Or the dream (vision) of Frodo in the House of Bombadil, which showed Frodo his possibly fate, that he will come to the Undying Lands.
This dreams are telling the future or the possibly future and Olórins visions are fair and giving hope.

The Silmarillion, Of the Maiar:
[i]But of Olórin that tale does not speak; for though he loved the Elves, he walked among them unseen, or in form as one of them, and they did not know whence came the fair visions or the promptings of wisdom that he put into their hearts. In later days he was the friend of all the Children of Ilúvatar, and took pity on their sorrows; and those who listened to him awoke from despair and put away the imaginations of darkness.[/i ]

But there was in eveery case a power of foresight in Middle-Earth. We know it from Galadriel and her mirror, which are very similar to the vision, which Frodo had. The seen things are not really the future, but they could it be.