Histogram type support in HistogramBase and remove SetRangeDescription function

base/metrics/sparse_histogram.cc

Index: base/metrics/sparse_histogram.cc
diff --git a/base/metrics/sparse_histogram.cc b/base/metrics/sparse_histogram.cc
index e4e16e82aea57422a7602f3839ce6ab36fd21ecc..169037dcca9c741bc40737b4c7d9e919a1340c46 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -26,6 +26,10 @@ HistogramBase* SparseHistogram::FactoryGet(const string& name, int32 flags) {
 
 SparseHistogram::~SparseHistogram() {}
 
+HistogramType SparseHistogram::GetHistogramType() const {
+  return SPARSE_HISTOGRAM;
+}
+
 bool SparseHistogram::HasConstructionArguments(Sample minimum,
                                                Sample maximum,
                                                size_t bucket_count) const {