Postmortem report collection: validate internal state

This change introduces checking of the underlying allocator's state
(initialized, deleted, corrupt, valid). Stability files are no longer deleted on clean exit but instead marked as deleted.

BUG=691595

Review-Url: https://codereview.chromium.org/2767193002
Cr-Commit-Position: refs/heads/master@{#466561}
9 files changed