+1 , i was thinking on this today (could be part of debugger set)
chrome for example can check how long each .js part is taking to complete(but you cant make alot out of it)
i guess it would be important to know what you want to profile and if its possible
i think in unity you can check how much overdraw there is in the scene by colorstrength,
others could be for example seeing just the collisionboxes..