Fix HAR validation for HAR viewer
diff --git a/lib/utils/har.py b/lib/utils/har.py
index 0dfe2a69342..7eb0a8bcb8b 100644
--- a/lib/utils/har.py
+++ b/lib/utils/har.py
@@ -72,7 +72,11 @@ def toDict(self):
             "request": self.request.toDict(),
             "response": self.response.toDict(),
             "cache": {},
-            "timings": {},
+            "timings": {
+                "send": -1,
+                "wait": -1,
+                "receive": -1,
+            },
             "time": int(1000 * (self.endTime - self.startTime)),
             "startedDateTime": "%s%s" % (datetime.datetime.fromtimestamp(self.startTime).isoformat(), time.strftime("%z")) if self.startTime else None
         }

Following the comment on #2618, I confirmed the errors are present. I've double-checked the specification and confirmed some of the properties are indeed required. I've added stubs for them which prevents the validation from complaining.