Are we entirely sure he gets scarred in a courtroom, though? It seems incredibly wasteful, and not to mention too coincidental, for Harvey to be lying on the ground with that specific half of his face drenched in gasoline, then seeing an explosion of a building Gordon is approaching, then seeing Gordon being fought to keep out of by his fellow officers.
Truthfully, it all seems fairly obvious. Dent makes a big move for Maroni, Maroni gets pissed, kidnaps him, and lights him ablaze inside a warehouse. Gordon gets a tip on where Maroni would be holding him, and arrives to arrest Maroni, but is too late as it explodes. Knowing his friend is inside, Gordon rushes to get in, but is pulled back by his fellow officers as Dent is left to burn. A couple of scenes later, and we're treated to this scene, as Dent makes a surprise re-appearance as Two-Face.
I think this acid business is simply Eckhart acknowledging Harvey's comic ordeals, so he doesn't have to spill what happens in the film, and how it differs.