build: drop ninja as dependency and use shared cipd script

[dumbmoron]

No description provided.

[greptile-apps]

The PR appears safe to merge based on the reviewed changes.

_{Reviews (1) · Last reviewed commit: "build: drop ninja as dependency and use ..."}

[helium-gardener]

Review completed with no actionable findings.

Review walkthrough

Changes

Files	Summary
docker/build.Dockerfile scripts/shared.sh helium/devutils/install_cipd_deps.py	Ninja is retained only where non-x86 LLVM/Rust builds require it; the shared CIPD installer now provisions host GN, Siso, and TypeScript before GN generation and the Siso build.
helium-chromium helium/patches/series patches/series	The submodule advance supplies the shared installer and related Helium updates. The Linux platform patches and their ordering are unchanged from the merge base, so their materialized additions do not represent new platform-patch intent.

Review checks

Check	Result	Notes
Scope	✅ Passed	Comparison against the merge base confirmed that the feature-template hunk in 'change.diff' is base-branch-only; the PR changes only the Dockerfile, shared build script, and submodule pointer.
Project Policy	✅ Passed	No upstream Chromium test file, case, data, expectation, or test target is modified by the reviewable change.
Correctness And Safety	✅ Passed	Tool provisioning order, failure propagation, host and cross-build architecture handling, and explicit Siso selection were checked without a discrepancy.
Chromium Idioms	✅ Passed	The shared installer reads pinned CIPD manifests through Chromium's 'gclient_eval' and installs the DEPS-owned locations consumed by Chromium's GN and Siso wrappers.
Simplicity And Decomposition	✅ Passed	The change removes duplicated CIPD version lookup and local GN bootstrap logic in favor of the shared Helium installer.
Patch Organization	✅ Passed	The unchanged Linux patch series remains prerequisite-ordered, and the submodule advance is required before 'scripts/shared.sh' can invoke the new installer.

Analysis record

• Changed files considered: 3
• Findings: 0 new, 0 retained, 0 resolved
• Source snapshot: 6af469f2607e
• Codex: gpt-5.6-sol, reasoning high, fast mode on, web search cached
• Patch application: clean
• Chromium context tool calls: none
• Maintainer conventions applied: script-resource-lifecycle

Limitations

• None reported.