Moving to a lazy test loading approach makes counting the total number of tests
non-trivial.

For CI runs, we output the total number of tests after the run.
For users, progress indicator signals the status of the run.

R=machenbach@chromium.org
CC=​yangguo@chromium.org,sergiyb@chromium.org

Bug: v8:8174
Change-Id: I0731964515aac60a3629acee6c7243433a2b4e04
Reviewed-on: https://chromium-review.googlesource.com/c/1420677
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58944}