This helps identify file IO. Unfortunately, with this marker, it's
difficult to separate code we own from code we don't own. However, I
wasn't sure what the best implementation would be to address that
(e.g. ideally, we would ignore violations in code we don't own rather than
annotate the markers) so I thought we can land it this simple way and
improve it incrementally.
While StrictMode is not exclusively used for performance purposes, it's
primarily used for perf purposes so let's move it to the perf package
and code owner it.
Grisha Kruglov