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/f3ef205b4f632c18d20eb83e7b5f6a0e3ca77b21