Add once field to devtools so it can be queried by lighthouse.

third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt

Index: third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt
diff --git a/third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt b/third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt
index a1d8b7c89f63c05da3ff9ed24f1c10e0bc13cea0..cb9f38374b059904be0f32be6ac6fe3b35469f89 100644
--- a/third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt
+++ b/third_party/WebKit/LayoutTests/http/tests/inspector/elements/event-listeners-framework-with-service-worker-expected.txt
@@ -13,6 +13,7 @@ Dumping listeners
 [expanded] WindowRemoveevent-listeners-framework-with-service-worker.html:59
     useCapture: false
     passive: false
+    once: false
     handler: function onload(event) {
   runTest()
 }