Add deprecation notice to BrowserThread::PostAfterStartupTask

Bug: 887407
Change-Id: I21777fedb072a12499c11c703c99228778eda280
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1571662
Commit-Queue: Carlos Caballero <carlscab@google.com>
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653127}
1 file changed