[worth]

I don't think the purpose of inciting riots would be to try out a new toy. My guess is it would be benificial to police and government for these reasons:

1) demonize protesters - media will play the tapes of huge riots and tear gas and such and all protesters will be painted with a broad brush that they are all trouble makers. the media doesn't really like to play tapes of peaceful protests. kind of boring.
2) this in turn allows governments and police the ability to say "ok, you can't protest here. this is no longer a protest zone, we'll move all the protesters out to this area where we can handle them better because they are violent"
3) general public will accept this reasoning after seeing violent riots
4) police budgets can be increased to handle these situations, governments can introduce new laws with more control over the public.
5) government could even suspend all protests and declare martial law over a city during a summit such as this one if they deem protests to be too dangerous. i wouldn't count this out from happening in the future. Have a couple cops die on the line and there you go.

But this is an extremly conspiratorial viewpoint and just a guess at why they would want to incite riots if they indeeed do at all. And i'm not at all saying this is what I believe is happening. Nothing has been proven. Show me a memo or other government/police document that says they are to incite riots to cause destabilizion to further an agenda.