Add missing dependency to bower.json

Author: TimvdLippe

bower.json

@@ -25,7 +25,8 @@
   },
   "devDependencies": {
     "web-component-tester": "^6.0.0",
-    "test-fixture": "PolymerElements/test-fixture#3.0.0-rc.1"
+    "test-fixture": "PolymerElements/test-fixture#3.0.0-rc.1",
+    "perf-tester": "polymerlabs/perf-tester"
   },
   "private": true,
   "resolutions": {