Electron Releases

Description of Change

pipeline-segment-build-siso needs the siso commit that our pinned Chromium expects. Until now it curled Chromium's DEPS from raw.githubusercontent.com on every run to find it, and that fetch has failed main several times recently (HTTP errors and a TLS reset; on 09-02 it took out all three siso jobs in one run). The value only changes when Chromium rolls, so this records it in the repo and removes the fetch entirely:

• build/siso_revision holds the sha. The build-siso job reads it from its sparse checkout; no network involved in resolving it any more.
• script/gen-siso-revision.js derives the value from the synced Chromium tree (siso_version in src/DEPS). It runs as a gen_siso_revision gclient hook after every sync, from lint-staged when DEPS changes, and with --check in the gn-check job so a roll that forgets to commit the updated file fails with a message saying exactly what to do.
• script/lint-roller-chromium-changes.mjs accepts a chore: update siso revision commit that touches only that file, and the Chromium upgrade skill/commit guidelines say to make that commit after a successful e sync --3 — same treatment as filenames.libcxx.gni.

Seeded with the revision for the currently pinned Chromium (155.0.8038.2 → efbbe7f18922…). Release branches keep the old curl step until this is backported.

Checklist

• I have built and tested this change
• I have filled out the PR description
• I have reviewed and verified the changes

Release Notes

Notes: none