[dev.garbage] runtime: ignore objects in dead spans
[dev.garbage] runtime: ignore objects in dead spans

We still don't know why this is happening.

LGTM=rlh
R=rlh
CC=golang-codereviews
https://codereview.appspot.com/169990043

webfd/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh