Summary: This helps avoid iterating through all trackers. The next diff will present an optimization where we reduce the number of iterations through the more expensive map.

Test Plan: Existing tests.

Reviewers: #stirling, yzhao

Reviewed By: #stirling, yzhao

Subscribers: yzhao

Differential Revision: https://phab.corp.pixielabs.ai/D8430

GitOrigin-RevId: 5d8f7a673d3951a09a16f20333b563d086b02436