What were the stone-giants doing in chapter 4 of The Hobbit?

You're thinking of Chapter 5 of The Hobbit, not Chapter 4. In Chapter 5, "Riddles in the Dark", the Stone-Giants are not explicitly described doing anything.

The chapter focuses on Bilbo's encounter with Gollum in the dark caverns beneath the Misty Mountains.

However, it's important to note that:

* The Stone-Giants are mentioned in the chapter, as Gollum warns Bilbo that they are dangerous and should be avoided.

* They are seen as a terrifying threat by Gollum, even more so than he fears the dwarves.

* Their presence is implied to be a significant aspect of the surrounding landscape and adds to the sense of danger in the story.

Therefore, while we don't see the Stone-Giants actively doing anything in Chapter 5, their presence looms over the events of the chapter and adds a layer of fear and mystery.