R1:46feccdfcf19

Share more inline "Done" code between Differential and Diffusion

Summary:
Ref T13222. See PHI995. Before making a change to inline rendering, consolidate this code for generating the "alice added inlines comments." and "alice marked X inlines as done." transactions.

Both Differential and Diffusion have four very similar chunks of code. Merge them into shared methods and reduce code duplication across the methods.

(In the next change, I plan to hide the "done" story when the mark affects your own inline…