IIUC, the point to have separate structs.rs and bindings.rs was because we have two structs files in the past, for debug and release build respectively. In bug 1400084 we stopped generating two structs.rs, but I forgot that we can also merge structs.rs into bindings.rs. We should probably do that here. It should help the build time of style crate since we would no longer need to scan all the headers twice.

I expect bug 1412486 to change some code in build_gecko.rs, so it's probably better holding on until that gets landed (since that should happen sooner).

status-firefox57=wontfix unless someone thinks this bug should block 57

P3 because this bug doesn't block us from shipping stylo-chrome or Android.