Makes it possible to get the expiry time of an origin trial feature.

This is needed for the upcoming file handling origin trial, which will
store state in the operating system, which needs to be cleaned up when
the trial expires.

WIP CL for the file handling origin trial:
https://crrev.com/c/1940001

Bug: 1028448
Change-Id: I3bc8b5cdb786ef17bc8a0360f99d7b07d0cfd4b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2010604
Reviewed-by: Jason Chase <chasej@chromium.org>
Commit-Queue: Jay Harris <harrisjay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734607}
6 files changed