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* BooleanHistogram::FactoryGet(const char* name, int32_t flags) {
  return FactoryGet(std::string(name), flags);
}

HistogramBase* BooleanHistogram::FactoryGet(const char* name, int32_t flags) {
  return FactoryGet(std::string(name), flags);
}
