Sync the browser test host resolver with the network process before a test runs.

content/network/manifest.json

 {
   "name": "network",
   "display_name": "Network Service",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
+        "test": [
+          "content::mojom::NetworkServiceTest"
+        ],
         "url_loader": [
           "content::mojom::URLLoaderFactory"
         ]
       },
       "requires": {
         "service_manager": [ "service_manager:all_users" ]
       }
     }
   }
 }