In chromium/src/base/histogram.cc, there are a few places where a histogram is deemed not valid, but the error is not logged.  For instance:

  if (*bucket_count > static_cast<uint32_t>(*maximum - *minimum + 2)) {
    check_okay = false;
    *bucket_count = static_cast<uint32_t>(*maximum - *minimum + 2);
  }
  
The cros metrics library does not make these checks, so it is possible to send cros histogram samples which are completely ignored.  This can cause problems when testing.  (See if you can guess who had such problems.)

Even if these errors were logged, it would be better to replicate these checks on the cros side.  The checks are intrinsic to the definition of the histograms, so the code duplication is acceptable.