Enable single hop screenshots for only threaded re

Fixes a deadlock where screenshot requests are blocked
on the main thread which inturn is blocked by the
screenshot request finishing.

Flag: EXEMPT bug fix
Bug: 349776684
Bug: 349741485
Bug: 352267188
Test: presubmit
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5aadd249f326b21e5ef6cadfebc15b6a0a016816)
Merged-In: Ibf038ad6db3e87c84508d3e101ca1eb144836d7c
Change-Id: Ibf038ad6db3e87c84508d3e101ca1eb144836d7c