Bug 1381470 - Added a less memory consuming method to tell if a histogram is empty. r=chutten

ipc/chromium/src/base/histogram.h

@@ -115,6 +115,10 @@ class Histogram {
 
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf);
 
+  bool is_empty() const {
+    return this->sample_.counts(0) == 0 && this->sample_.sum() == 0;
+  }
+
   //----------------------------------------------------------------------------
   // Statistic values, developed over the life of the histogram.
 

toolkit/components/telemetry/TelemetryHistogram.cpp

@@ -335,9 +335,7 @@ internal_CanRecordExtended() {
 bool
 internal_IsEmpty(const Histogram *h)
 {
-  Histogram::SampleSet ss;
-  h->SnapshotSample(&ss);
-  return ss.counts(0) == 0 && ss.sum() == 0;
+  return h->is_empty();
 }
 
 bool