Add perf test for null-aggregatable-report generation

Change-Id: Iaf9eb78176d3c9c8a19d6dacf4c6a406998cb602
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5434813


Commit-Queue: Andrew Paseltiner <apaseltiner@chromium.org>
Reviewed-by: Nan Lin <linnan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283847}