https://code.google.com/p/chromium/codesearch#chromium/src/third_party/zlib/google/zip_reader.cc&l=169&cl=GROK

  if (exploded_time.HasValidValues()) {
    last_modified_ = base::Time::FromLocalExploded(exploded_time);
  } else {
    // Use Unix time epoch if the time stamp data is invalid.
    last_modified_ = base::Time::UnixEpoch();
  }

However HasValidValues() is not guaranteed to mean that FromLocalExploded() succeeds.