Bug 1436244 - Make default allowed leaks for mozilla wpt tests match those for upstream tests, a=testonly

testing/web-platform/mozilla/meta/__dir__.ini

@@ -1,3 +1,6 @@
 lsan-allowed: [Init, nsHostResolver::ResolveHost]
 leak-threshold:
-  [rdd:400]
+  if webrender: [tab:10000, geckomediaplugin:20000, default:16000]
+  if os == "mac": [tab:10000, geckomediaplugin:20000, default:2000, rdd:400]
+  [tab:10000, geckomediaplugin:20000, rdd:400]
+