Bug 1437689 - Add basic memory reporting for gNameToHistogramIDMap. r=gfritzsche

MozReview-Commit-ID: 8QGudRuXmWh

--HG--
extra : rebase_source : a2334b2f434337f1551a9d13c2ad0a9c23a6de7b

toolkit/components/telemetry/TelemetryHistogram.cpp

@@ -2388,8 +2388,7 @@ TelemetryHistogram::GetMapShallowSizesOfExcludingThis(mozilla::MallocSizeOf
                                                       aMallocSizeOf)
 {
   StaticMutexAutoLock locker(gTelemetryHistogramMutex);
-  // TODO
-  return 0;
+  return gNameToHistogramIDMap.ShallowSizeOfExcludingThis(aMallocSizeOf);
 }
 
 size_t