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}
HistogramBase* Histogram::FactoryTimeGet(const std::string& name,
                                         TimeDelta minimum,
                                         TimeDelta maximum,
                                         uint32_t bucket_count,
                                         int32_t flags) {
  return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
                    static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
                    flags);
}

HistogramBase* Histogram::FactoryTimeGet(const std::string& name,
                                         TimeDelta minimum,
                                         TimeDelta maximum,
                                         uint32_t bucket_count,
                                         int32_t flags) {
  return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
                    static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
                    flags);
}
