Repro:

1) Launch chrome with --site-per-process
2) navigate to http://scheib.github.io/HTMLMisc/PointerLockAndFullscreen-iframes.html
3) click on the first "Fullscreen & Lock Pointer Target1".
4) Notice that the mouse coordinates don't change.

This only happens when Fullscreen + Pointer lock is done at the same time. When just entering pointer lock, it works fine, when entering fullscreen, then locking the pointer, it also works fine.