[perf] Add load:search:google:2018 system health story

This CL was created automatically with tools/perf/update_wpr script
Bug: 878390
R=perezju@chromium.org

Change-Id: I65300d654439ed65591691f5881cd8b1002c913c
Reviewed-on: https://chromium-review.googlesource.com/c/1329665
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608101}