Bug 1447655 - Only run dom/tests/browser/browser_test_performance_metrics.js on Nightly. r=baku

MozReview-Commit-ID: CXNUcG5ml1J

--HG--
extra : rebase_source : f6e693c92dfe2fe65389ebff6b97f359cae5be0e

dom/tests/browser/browser.ini

@@ -73,3 +73,4 @@ support-files =
   test_noopener_target.html
 [browser_noopener_null_uri.js]
 [browser_test_performance_metrics.js]
+run-if = nightly_build