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}
  Factory(const std::string& name,
          const std::vector<Sample>* custom_ranges,
          int32_t flags)
    : Histogram::Factory(name, CUSTOM_HISTOGRAM, 0, 0, 0, flags) {
    custom_ranges_ = custom_ranges;
  }

  Factory(const std::string& name,
          const std::vector<Sample>* custom_ranges,
          int32_t flags)
    : Histogram::Factory(name, CUSTOM_HISTOGRAM, 0, 0, 0, flags) {
    custom_ranges_ = custom_ranges;
  }
