Convert DCHECKs to CHECKs for histogram types

When a histogram is looked up by name, there is currently a DCHECK that
verifies the type of the stored histogram matches the expected type.

A mismatch represents a significant problem because the returned
HistogramBase is cast to a Histogram in ValidateRangeChecksum,
potentially causing a crash.

This CL converts the DCHECK to a CHECK to prevent the possibility of
type confusion in release builds.

BUG=651443
R=isherman@chromium.org

Review-Url: https://codereview.chromium.org/2381893003
Cr-Commit-Position: refs/heads/master@{#421929}
uint32_t Histogram::FindCorruption(const HistogramSamples& samples) const {
  int inconsistencies = NO_INCONSISTENCIES;
  Sample previous_range = -1;  // Bottom range is always 0.
  for (uint32_t index = 0; index < bucket_count(); ++index) {
    int new_range = ranges(index);
    if (previous_range >= new_range)
      inconsistencies |= BUCKET_ORDER_ERROR;
    previous_range = new_range;
  }

  if (!bucket_ranges()->HasValidChecksum())
    inconsistencies |= RANGE_CHECKSUM_ERROR;

  int64_t delta64 = samples.redundant_count() - samples.TotalCount();
  if (delta64 != 0) {
    int delta = static_cast<int>(delta64);
    if (delta != delta64)
      delta = INT_MAX;  // Flag all giant errors as INT_MAX.
    if (delta > 0) {
      UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountHigh", delta);
      if (delta > kCommonRaceBasedCountMismatch)
        inconsistencies |= COUNT_HIGH_ERROR;
    } else {
      DCHECK_GT(0, delta);
      UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountLow", -delta);
      if (-delta > kCommonRaceBasedCountMismatch)
        inconsistencies |= COUNT_LOW_ERROR;
    }
  }
  return inconsistencies;
}

uint32_t Histogram::FindCorruption(const HistogramSamples& samples) const {
  int inconsistencies = NO_INCONSISTENCIES;
  Sample previous_range = -1;  // Bottom range is always 0.
  for (uint32_t index = 0; index < bucket_count(); ++index) {
    int new_range = ranges(index);
    if (previous_range >= new_range)
      inconsistencies |= BUCKET_ORDER_ERROR;
    previous_range = new_range;
  }

  if (!bucket_ranges()->HasValidChecksum())
    inconsistencies |= RANGE_CHECKSUM_ERROR;

  int64_t delta64 = samples.redundant_count() - samples.TotalCount();
  if (delta64 != 0) {
    int delta = static_cast<int>(delta64);
    if (delta != delta64)
      delta = INT_MAX;  // Flag all giant errors as INT_MAX.
    if (delta > 0) {
      UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountHigh", delta);
      if (delta > kCommonRaceBasedCountMismatch)
        inconsistencies |= COUNT_HIGH_ERROR;
    } else {
      DCHECK_GT(0, delta);
      UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountLow", -delta);
      if (-delta > kCommonRaceBasedCountMismatch)
        inconsistencies |= COUNT_LOW_ERROR;
    }
  }
  return inconsistencies;
}
