Implement a lock free version of RolloverProtectedTickClock::Now
to eliminate a deadlock.

BUG=chromium:521420
LOG=Y

Committed: https://crrev.com/d6db8e5902af1f067f0f149844f4e92824ee93f3
Cr-Commit-Position: refs/heads/master@{#30489}

Review URL: https://codereview.chromium.org/1304873011

Cr-Commit-Position: refs/heads/master@{#30522}