Previously we were only regenerating the commit ID when the .git/HEAD
file changed. When working on a branch the HEAD file doesn't change.
It points to a ref like refs/heads/master that changes. So we can read
back the contents of .git/HEAD using GN's read_file command and then
mark the commit id as dirty when the ref changes.
Should alleviate some of the shader cache problems.
Bug: angleproject:4448
Change-Id: I1c39b12af3455e3620d80bec92a15f9921d9163b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2358519Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
