R1:6d9b94bcb11a

Fix clone input on device breakpoints in Diffusion

Summary: The float wasn't getting reset on the definition list, so clone URI (so important on mobile!) looked terrible.

Test Plan: Tested Diffusion, Herald, and Maniphest property lists. Seems good.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12331