Consolidate calls to clock sources to OfflineClock #1

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:

chrome/browser/android/explore_sites/
components/offline_pages/core/model/

Bug: 906903
Change-Id: I02b84f65b77dc395310995c34ded41d92721aaeb
Reviewed-on: https://chromium-review.googlesource.com/c/1352813
Reviewed-by: Cathy Li <chili@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Dan H <harringtond@google.com>
Commit-Queue: Mark Lieu <mtlieuu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614797}
19 files changed