When review UIs for binary files are rendered in "inline" mode as part

of the diff viewer, the serialized comments are included in the rendered

fragment (as opposed to comments on regular diff files, which are all

included as part of the main diff viewer page). Our ETag calculation

wasn't taking this into account, which meant that after making changes

to comments (adding, removing, editing), reloading the diff viewer could

show outdated comments coming from the browser cache.
This change reworks the fragment view to include all comment timestamps

in the ETag when the filediff in question is binary. We had an existing,

similar example in CommentDiffFragmentsView that included the latest

timestamp in the ETag, but this is broken in the case where comments are

deleted or edited on a pending review. I've changed that to include the

same behavior of including all comment timestamps rather than just the

latest.
A couple new tests have been added to verify the cache response

behavior.

Ran unit tests.
Verified that comments on binary files in the diff viewer no longer

  presented with outdated browser cache bugs.