Some people have already made this comparison. But the only real point of comparison is that once the media established a narrative, facts don't matter. Here the narrative is that some cop shot Brown because...well for no reason at all. In Martn's case some white Hispanic guy shot Martin because he didnt like the looks of him. Both narratives are completely wrong, not even believable. But it doesnt matter. People will insist those are the true accounts and they will dismiss, or rationalize away any contrary evidence.
The case of Trayvon Martin is completely different. There Zimmmerman shouldn't have had his gun with him (I don't give a shit it was legal he had it with him). If he didn't have his unnecessary gun, both would have been arrested because there were no witnesses who could verify who started the right. The facts after that would have decided who should be punished. Instead someone died for no good reason.
This Brown story is nothing like that. We have to wait for the official report but given what we know now I think it is likely the cop shot him in self defense. Obviously the cop should have been carrying his gun regardless. What will really matters is how the IA report went.