[Tests] Update InvalidationsHandler reset to reset invalidationCountForEvent too

Otherwise, state of the `invalidationCountForEvent` is leaking
between different tests.

Bug: none
Change-Id: Ic4a865c6662010ff2da2ef1b447c80a36abf721c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6366900
Reviewed-by: Paul Irish <[email protected]>
Reviewed-by: Jack Franklin <[email protected]>
Commit-Queue: Jack Franklin <[email protected]>

Author: ergunsh

front_end/models/trace/handlers/InvalidationsHandler.ts

@@ -16,6 +16,7 @@ const allInvalidationTrackingEvents: Types.Events.InvalidationTrackingEvent[] =
 
 export function reset(): void {
   invalidationsForEvent.clear();
+  invalidationCountForEvent.clear();
   lastRecalcStyleEvent = null;
   allInvalidationTrackingEvents.length = 0;
   hasPainted = false;