Connect SparseHistogram with the rest of stats system

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 c64f7cb1c649dff13de20a8a9ed04e3a320a1973..295267335a4efd6fb595c895ffdc93706a06500f 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -19,9 +19,16 @@ typedef HistogramBase::Sample Sample;
 
 // static
 HistogramBase* SparseHistogram::FactoryGet(const string& name, int32 flags) {
-  // TODO(kaiwang): Register and get SparseHistogram with StatisticsRecorder.
-  HistogramBase* histogram = new SparseHistogram(name);
-  histogram->SetFlags(flags);
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
+
+  if (!histogram) {
+    // To avoid racy destruction at shutdown, the following will be leaked.
+    HistogramBase* tentative_histogram = new SparseHistogram(name);
+    tentative_histogram->SetFlags(flags);
+    histogram =
+        StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
+  }
+  DCHECK_EQ(SPARSE_HISTOGRAM, histogram->GetHistogramType());
   return histogram;
 }