Replace OfflineClock()->Now() with OfflineTimeNow()

This change is for consistency, and simplicity: most code doesn't need to access
OfflineClock() for more than the current time.

Bug: 906903
Change-Id: I34597e40c8e3a0d450867beb19ce602b8afd7d72
Reviewed-on: https://chromium-review.googlesource.com/c/1372270
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Dan H <harringtond@google.com>
Cr-Commit-Position: refs/heads/master@{#616377}
49 files changed