pageload_benchmark.py turns Macrobenchmark output into per-scenario stats and, optionally, reports them as a m_page_load_time_android pixel.

trace_processor_shell — not a pip package, a standalone Perfetto binary that must be on PATH separately. The script fails with a clear error if it's missing, but does not install it. To install:

curl -LO https://get.perfetto.dev/trace_processor
chmod +x ./trace_processor
sudo mv ./trace_processor /usr/local/bin/trace_processor_shell

1. Discover — given an FTL/Flank results directory, find every PageLoadBenchmark entry across all *benchmarkData.json files and match each one to its .perfetto-trace by filename. Requires exactly the six scenarios in SCENARIO_BY_BENCHMARK_NAME (no-trackers, many-trackers-blocked, first-party-trackers, cpm, all-protections-on, all-protections-off) — missing, duplicate, or unexpected scenarios abort the whole run. The two all-protections-* scenarios run the same fixture with DuckDuckGo protections enabled and disabled respectively, so they're directly comparable to each other.
2. Extract — query each trace for ddg.pageLoad slice durations via trace_processor_shell (must be on PATH; see below).
3. Compute stats — drop the leading warmup sample and the trailing sentinel sample by position, then report count, median, mean, std_dev, min, max, p90 over the remaining samples.
4. Report — with --report-pixel, build one pixel URL per scenario and send it. Refuses to send anything unless all six scenarios validated successfully (no partial reporting).

# Process a full FTL/Flank results directory, print + write combined stats
python3 pageload_benchmark.py --results-dir /path/to/results

# Same, and report pixels
python3 pageload_benchmark.py --results-dir /path/to/results \
  --report-pixel --github-action-run-id 123 --git-commit-sha abcdef

# Process a single trace (e.g. for local debugging one scenario)
python3 pageload_benchmark.py --trace some.perfetto-trace --scenario cpm

--trace mode requires --scenario and cannot be combined with --report-pixel (only --results-dir validates all six scenarios atomically, so it's the only mode allowed to send pixels).