Address jack's additional comments in code review
Address jack's additional comments in code review

Test Plan:
- Load my modified test.html, check iframe to see that it has origin=localhost appended to its URL

Auditors: jack

abe4mvp/perseus,chirilo/perseus,ariabuckles/perseus,daukantas/perseus,junyiacademy/perseus,ariabuckles/perseus,chirilo/perseus,huangins/perseus,junyiacademy/perseus,iamchenxin/perseus,learningequality/perseus,abe4mvp/perseus,daukantas/perseus,learningequality/perseus,alexristich/perseus,sachgits/perseus,alexristich/perseus,huangins/perseus,sachgits/perseus,ariabuckles/perseus,ariabuckles/perseus,iamchenxin/perseus