R1:0a749ad51b69

Give unposted comments a distinct visual style

Summary:
See attached tasks. See D459 for the ability to merge tasks.

Test Plan:
Looked at posted and unposted inline comments.

Reviewed By: aran
Reviewers: edward, viyer, aran, jungejason, tuomaspelkonen
CC: aran, epriestley
Differential Revision: 461