John "codefu" McDole eb786c8c49
fix: get content hash for master on local engine branches (#173114)
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards #171790

re-land attempt for #172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.
2025-08-01 20:35:26 +00:00
..