R1:77250cd54cc0

Allow Multimeter samples to be grouped by ID

Summary: Ref T6930. This allows samples to be split apart even if they occurred in the same request.

Test Plan: {F391657}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6930

Differential Revision: https://secure.phabricator.com/D12676