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}
  size_t GetSnapshotHistogramCount() {
    provider()->MergeHistogramDeltas();

    HistogramFlattenerDeltaRecorder flattener;
    base::HistogramSnapshotManager snapshot_manager(&flattener);
    base::StatisticsRecorder::PrepareDeltas(true, base::Histogram::kNoFlags,
                                            base::Histogram::kNoFlags,
                                            &snapshot_manager);
    return flattener.GetRecordedDeltaHistogramNames().size();
  }

  size_t GetSnapshotHistogramCount() {
    provider()->MergeHistogramDeltas();

    HistogramFlattenerDeltaRecorder flattener;
    base::HistogramSnapshotManager snapshot_manager(&flattener);
    base::StatisticsRecorder::PrepareDeltas(true, base::Histogram::kNoFlags,
                                            base::Histogram::kNoFlags,
                                            &snapshot_manager);
    return flattener.GetRecordedDeltaHistogramNames().size();
  }
