Events codelab. Part 7. Add summary
Events codelab. Part 7. Add summary

Reviewed By: mihaelao

Differential Revision: D15965313

fbshipit-source-id: 65f0b3db16f56e6b272d2b6e8eab78768102a1c8

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho