Bug 1519454 - Put malloc_size_of_derive on crates.io, and add a reduc…
…ed fork of malloc_size_of for WebRender. r=emilio Differential Revision: https://phabricator.services.mozilla.com/D16353 [wrupdater] From https://hg.mozilla.org/mozilla-central/rev/d5e192fd022fd4ced320499ba7d2f0229b9fa9f2