Reorganize histograms for persistence.
This is split from cl/1425533011. It does all the base work
to support holding histograms in persistent memory including
moving some files so they'll be accessible and separating
metadata for external storage.
BUG=546019
TBR=danakj
(for trivial change to base/test/histogram_tester.cc)
Review URL: https://codereview.chromium.org/1471073007
Cr-Commit-Position: refs/heads/master@{#364408}
CrOS-Libchrome-Original-Commit: b036e43221eac3ca8a22d7e96258ca056444cedd
19 files changed