I'm going with "A Sky Full of Stars" as that's the only one I've heard of (even if it was in a commercial), but I think a sadder and/or darker song like "Rain" or "Circles" by Hollywood Undead (no, those songs are not metal or full of profanity) would fit the tone of the movie better. Maybe even "Final Masquerade" or "Not Alone" by Linkin Park.

Rain: link
Circles: link
Final Masquerade: link
Not Alone: link