Previously, gr-diff-preferences was the contents that was displayed in
an overlay contained in the gr-diff-view. There were a handful of
functions that crossed between the two-- the diff preferences element
would fire events that needed to be handled by the diff view.
Because the gr-diff-preferences element will be added to the change
view as well, the overlay has been moved to be part of the diff
preferences element. This way, the element can handle all of the actions
taken by the panel, and all the parent element needs to do is call
the open function.
A separate change will come with the addition of diff preferences in the
change view.
Bug: Issue 5426
Change-Id: Id7396147e73354122ea3825bde2c324b5daa1d26
7a45400e24