Bug 1515486 - Set a leak threshold for the gpu process on WR-enabled WPT tests. r=jmaher

Differential Revision: https://phabricator.services.mozilla.com/D15223

--HG--
extra : moz-landing-system : lando

testing/web-platform/meta/__dir__.ini

@@ -1,6 +1,6 @@
 lsan-allowed: [js_pod_malloc, js_pod_calloc, js_pod_realloc, js_arena_calloc,js_pod_arena_calloc, maybe_pod_calloc, pod_calloc, make_zeroed_pod_array, js_arena_malloc]
 leak-threshold:
-  if webrender: [tab:10000, geckomediaplugin:20000, default:16000]
+  if webrender: [tab:10000, gpu: 10000, geckomediaplugin:20000, default:16000]
   if os == "mac": [tab:10000, geckomediaplugin:20000, default:2000, rdd:400]
   [tab:10000, geckomediaplugin:20000, rdd:400]