GitLab

The DelayedPersistentAllocation added an atomic field to the
PersistentHistogramData structure that cannot be copied using
operator= (at least not without redefining it).  Copies of only
some of the fields are needed so explicitly copy only those; the
atomic field is not one of them.

BUG=721352

Review-Url: https://codereview.chromium.org/2875643004
Cr-Commit-Position: refs/heads/master@{#471143}