PSA: things are changing on many of the chromium builders

[Dirk Pranke]

Hi all,

As part of the home stretch on the GYP->GN migration we've been making a bunch of changes to the chromium bots this

week to ensure that they're all running the 'MB' wrapper that lets us flip between GYP and GN via src-side changes that

can be tested through the trybots (at least for the bots that have matching trybots). In theory these changes should

not effect what is getting compiled or tested, but it's possible we've made mistakes.

I've also used this as an excuse to do some spring cleaning and shut down or moved a number of bots, mostly on the 

FYI waterfalls. So, if some bot you care about has suddenly disappeared, you likely know who to blame.

I think things are mostly normal at this point (I'm not aware of any errors), but if you see anything amiss on bots you

care about (in particular, bad sets of GYP_DEFINES or strange compiler errors), let me know.

-- Dirk