Optimizations to histogram protobuf encoding.

components/metrics/histogram_encoder.cc

Index: components/metrics/histogram_encoder.cc
diff --git a/components/metrics/histogram_encoder.cc b/components/metrics/histogram_encoder.cc
index f816807db92eeda67c55a862fc7d101e12ae8e4f..58cd01c83b469d6db0bec12af419ff7eec540389 100644
--- a/components/metrics/histogram_encoder.cc
+++ b/components/metrics/histogram_encoder.cc
@@ -25,7 +25,8 @@ void EncodeHistogramDelta(const std::string& histogram_name,
 
   HistogramEventProto* histogram_proto = uma_proto->add_histogram_event();
   histogram_proto->set_name_hash(base::HashMetricName(histogram_name));
-  histogram_proto->set_sum(snapshot.sum());
+  if (snapshot.sum() != 0)
+    histogram_proto->set_sum(snapshot.sum());
 
   for (scoped_ptr<SampleCountIterator> it = snapshot.Iterator(); !it->Done();
        it->Next()) {
@@ -36,7 +37,8 @@ void EncodeHistogramDelta(const std::string& histogram_name,
     HistogramEventProto::Bucket* bucket = histogram_proto->add_bucket();
     bucket->set_min(min);
     bucket->set_max(max);
-    bucket->set_count(count);
+    if (count != 1)

[rkaplow, 2016/02/29 22:46:44]

Might just add a comment that 1 is the default in the proto. Less worried about
sum since 0 is a pretty natural default but 1 is not so looks slightly odd.

[Alexei Svitkine (slow), 2016/02/29 22:55:53]

Done.

+      bucket->set_count(count);
   }
 
   // Omit fields to save space (see rules in histogram_event.proto comments).