Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram_base.cc

Index: base/metrics/histogram_base.cc
diff --git a/base/metrics/histogram_base.cc b/base/metrics/histogram_base.cc
index 412f1438d2fbde0b04a35c863dcba8b0e8e954dc..4f33dd252eed2b5dd84c98543530c5e9131d93d5 100644
--- a/base/metrics/histogram_base.cc
+++ b/base/metrics/histogram_base.cc
@@ -97,7 +97,7 @@ bool HistogramBase::SerializeInfo(Pickle* pickle) const {
   return SerializeInfoImpl(pickle);
 }
 
-int HistogramBase::FindCorruption(const HistogramSamples& samples) const {
+unsigned HistogramBase::FindCorruption(const HistogramSamples& samples) const {
   // Not supported by default.
   return NO_INCONSISTENCIES;
 }