Override Iterator::count method for vec::IntoIter

[sinkuu]

Override methods count, last, and nth in vec::IntoIter.
#24214

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[nwin]

If I’m not mistaken last will lead to a double-free of the last element and nth will leak everything until n.

[sinkuu]

@nwin Oops. Thanks for pointing that out! I'll update this pull request to override only count.

[alexcrichton]

@bors: r+ 5d8431c rollup

Thanks!

[bors]

⌛ Testing commit 5d8431c with merge 6517a0e...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt