If Android Repository removes an older version of the NDK, gclient sync breaks on engine. #27967
Description
I was aware this could happen, but assumed it would not happen often and that it might be a good thing. Looking back, I'm not sure that was the best choice and want to discuss how we can do better here.
The android_sdk_downloader tool uses https://dl.google.com/android/repository/repository2-1.xml to determine what packages are actually available and where it can download them from. If a package disappears from that list, we will fail. On the one hand that can be good - it forces us to stay up to date on the Android NDK. On the other, it can be bad if a developer or bot suddenly can't build the engine because the Android NDK version is no longer available (even though the NDK might still be available locally in third_party).
I would like to see us at least get a warning if a newer NDK is available. Supporting downloading older versions though may not be a trivial refactor short of us going back to maintaining a CIPD-like (or actual CIPD) bundle of Android artifacts.
/cc @cbracken @jason-simmons @chinmaygarde @liyuqian @GaryQian @Hixie
related: #27963