Also adds a simple unit test checking the pruning BUG=angleproject:937 BUG=395048 Change-Id: I88440378f66178dcebebcd596f8f80235903f20e Reviewed-on: https://chromium-review.googlesource.com/264568Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>
