[Osmosis] Move stable portability history parsing to background thread

This CL moves the parsing of the history file from the main thread
to the background thread.

Bug: 430253028

Change-Id: Id86da83313b71f9790c7eb65eca99b40f45ee15b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6787827
Commit-Queue: Michael Tatarski <mtatarski@google.com>
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Auto-Submit: Michael Tatarski <mtatarski@google.com>
Cr-Commit-Position: refs/heads/main@{#1492820}