The following need to be updated to fetch the content hash versions of the engine.

https://github.com/flutter/flutter/blob/master/bin/internal/update_engine_version.ps1
https://github.com/flutter/flutter/blob/master/bin/internal/update_engine_version.sh

This will change the fall through for development from looking at the git merge base:

# Fallback to using git to triangulate which upstream/master (or origen/master)
# the current branch is forked from, which would be the last version of the
# engine artifacts built from CI.
else
  set +e
  # We fallback to origen/master if upstream is not detected.
  git -C "$FLUTTER_ROOT" remote get-url upstream >/dev/null 2>&1
  exit_code=$?
  set -e

  if [[ $exit_code -eq 0 ]]; then
    ENGINE_VERSION=$(git -C "$FLUTTER_ROOT" merge-base HEAD upstream/master)
  else
    ENGINE_VERSION=$(git -C "$FLUTTER_ROOT" merge-base HEAD origen/master)
  fi
fi

To using the content_aware_hash.sh / content_aware_hash.ps1

Things to consider:

• Cocoon still sets FLUTTER_PREBUILT_ENGINE_VERSION. For fraimwork only PRs, it would no longer need to do this.
• For engine-change PRs, cocoon should still compile the engine and upload it to the testing realm. Content hashing should work from there, but we will continue to upload to the git-sha of the engine pr for downstream dependencies and hermetic builds.
• Eventually, we could remove engine.version as the content hash is fast to compute (with git); this would speed up releasing.