Bug 1197966 - Fix typo when releasing content-side probes in PerformanceStats-content.js. r=felipe

toolkit/components/perfmonitoring/PerformanceStats-content.js

@@ -79,8 +79,9 @@ Services.cpmm.addMessageListener("performance-stats-service-release", function(m
   if (!isContent) {
     return;
   }
+
   // Keep only the probes that do not appear in the payload
-  let probes = gMonitor.getProbeNames
+  let probes = gMonitor.probeNames
     .filter(x => msg.data.payload.indexOf(x) == -1);
   gMonitor = PerformanceStats.getMonitor(probes);
 });