Consolidate calls to clock sources to OfflineClock #3

This change further changes direct calls to Time::Now or the default
base::Clock instance to an OfflineClock module within classes which
need a Clock pointer to be passed into the class. This eliminates the
need for testing-only functions and further allows ease of testing.
This change is specific to production files and their related tests in:

components/offline_pages/core/

Bug: 906903
Change-Id: I579d9b8e9c785e0c004ecc3d25e05f7aa031fe4c
Reviewed-on: https://chromium-review.googlesource.com/c/1359487
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Commit-Queue: Mark Lieu <mtlieuu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614549}
6 files changed