[FileSystem] Harden against overflows of OperationID a bit better.

Rather than having a UAF when OperationID overflows instead overwrite
the old operation with the new one. Can still cause weirdness, but at
least won't result in UAF. Also update OperationID to uint64_t to
make sure we don't overflow to begin with.

TBR=mek@chromium.org

(cherry picked from commit b38064dbb21aaf32151073dcb7d594b240c68f73)

Bug: 925864
Change-Id: Ifdf3fa0935ab5ea8802d91bba39601f02b0dbdc9
Reviewed-on: https://chromium-review.googlesource.com/c/1441498
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#627115}
Reviewed-on: https://chromium-review.googlesource.com/c/1447265
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/branch-heads/3683@{#82}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
2 files changed