MB: Add webrtc_perf_tests to gn_isolate_map.pyl

BUG=chromium:687890
NOTRY=True

Review-Url: https://codereview.webrtc.org/2766513006
Cr-Commit-Position: refs/heads/master@{#17340}
diff --git a/tools-webrtc/mb/gn_isolate_map.pyl b/tools-webrtc/mb/gn_isolate_map.pyl
index 68e8032..cc46319 100644
--- a/tools-webrtc/mb/gn_isolate_map.pyl
+++ b/tools-webrtc/mb/gn_isolate_map.pyl
@@ -103,4 +103,8 @@
     "label": "//webrtc:webrtc_nonparallel_tests",
     "type": "non_parallel_console_test_launcher",
   },
+  "webrtc_perf_tests": {
+    "label": "//webrtc:webrtc_perf_tests",
+    "type": "console_test_launcher",
+  },
 }