What action in scene 3 has Romeo's dream from scene 1 foreshadowed?

If you meant Act 5, things are pretty dark. In act one he says,

I fear, too early: for my mind misgives

Some consequence yet hanging in the stars

Shall bitterly begin his fearful date

With this night's revels and expire the term

Of a despised life closed in my breast

By some vile forfeit of untimely death.

Romeo gets it pretty much bang on in act one!