Remove typically unused local_metadata_ field.
The vast majority of histograms and their samples are now "persistent"
with the memory coming from a special memory segment. It's wasteful to
have a "local metadata" structure in each sample object that is never
used.
Instead, allocate the structure from the heap for only those objects
that need it and release it when those objects get destructed.
BUG=733380
Review-Url: https://codereview.chromium.org/2973603002
Cr-Commit-Position: refs/heads/master@{#484282}
CrOS-Libchrome-Original-Commit: b4d87bb384bfc8b43cadc24160c0da01ab09f555
5 files changed