Remove UMA.CreatePersistentHistogram.Result

This histogram isn't showing anything meaningful and the problems it
could show are better observed by looking at the allocators directly.

Bug: 831013
Change-Id: Ibe968597758230192e53a7675e7390e968c9e5b9
Reviewed-on: https://chromium-review.googlesource.com/1008047
Commit-Queue: Brian White <bcwhite@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549986}
std::unique_ptr<HistogramBase> PersistentHistogramAllocator::GetHistogram(
    Reference ref) {
  PersistentHistogramData* data =
      memory_allocator_->GetAsObject<PersistentHistogramData>(ref);
  const size_t length = memory_allocator_->GetAllocSize(ref);

  if (!data || data->name[0] == '\0' ||
      reinterpret_cast<char*>(data)[length - 1] != '\0' ||
      data->samples_metadata.id == 0 || data->logged_metadata.id == 0 ||
      (data->logged_metadata.id != data->samples_metadata.id &&
       data->logged_metadata.id != data->samples_metadata.id + 1) ||
       HashMetricName(data->name) != data->samples_metadata.id) {
     NOTREACHED();
     return nullptr;
   }
  return CreateHistogram(data);
}

std::unique_ptr<HistogramBase> PersistentHistogramAllocator::GetHistogram(
    Reference ref) {
  PersistentHistogramData* data =
      memory_allocator_->GetAsObject<PersistentHistogramData>(ref);
  const size_t length = memory_allocator_->GetAllocSize(ref);

  if (!data || data->name[0] == '\0' ||
      reinterpret_cast<char*>(data)[length - 1] != '\0' ||
      data->samples_metadata.id == 0 || data->logged_metadata.id == 0 ||
      (data->logged_metadata.id != data->samples_metadata.id &&
       data->logged_metadata.id != data->samples_metadata.id + 1) ||
       HashMetricName(data->name) != data->samples_metadata.id) {
    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_METADATA);
     NOTREACHED();
     return nullptr;
   }
  return CreateHistogram(data);
}
