Similar to this question, I have seen in a lot of pro-replays players seemingly chronoboosing all 8 of their warp gates simultaneously.
Usually when I do it, I hot-key nexus, hot-key chronoboost, click gateway. But the in the replays, it seems as if it is done simultaneously because the chronoboost animations are synced on a large amount of gateways.
In order to accomplish this, you hold down the Shift Key with your Nexus selected (or nexuses), press C and continue to hold down the shift key and then click on each gateway. It's not simultaneous, but it is as fast as you can click, move, and click again. It does remove the requirement to keep hitting C to chronoboost each gateway though.
It appears to be simultaneous because the pros do it so fast.
In addition to the shift-click mechanic, being able to chrono-boost buildings via the minimap would contribute greatly to bringing about a simultaneous chrono across all of your gateways. It requires a bit of practice to get used to accurately clicking on buildings from the minimap (especailly in tense situations), but learning this skill will speed up your macro considerably.
