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}
  void InitializeStatisticsRecorder() {
    DCHECK(!statistics_recorder_);
    statistics_recorder_ = StatisticsRecorder::CreateTemporaryForTesting();
    auto record_checker = std::make_unique<TestRecordHistogramChecker>();
    StatisticsRecorder::SetRecordChecker(std::move(record_checker));
  }

  void InitializeStatisticsRecorder() {
    DCHECK(!statistics_recorder_);
    statistics_recorder_ = StatisticsRecorder::CreateTemporaryForTesting();
    auto record_checker = std::make_unique<TestRecordHistogramChecker>();
    StatisticsRecorder::SetRecordChecker(std::move(record_checker));
  }
