[MemCache] Fix bug while iterating LRU list in eviction

It was possible to reanalyze a previously doomed entry.

Bug: 827492
Change-Id: I5d34d2ae87c96e0d2099e926e6eb2c1b30b01d63
Reviewed-on: https://chromium-review.googlesource.com/987919
Commit-Queue: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547236}
int MemBackendImpl::DoomEntriesSince(Time initial_time,
                                     const CompletionCallback& callback) {
  return DoomEntriesBetween(initial_time, Time::Max(), callback);
}

int MemBackendImpl::DoomEntriesSince(Time initial_time,
                                     const CompletionCallback& callback) {
  return DoomEntriesBetween(initial_time, Time::Max(), callback);
}
