This changes the way the change list view is layed out (flexbox
instead of tables) for a couple reasons:
+ Table elements (td, tr, etc.) cannot be arbitrarily appended
to just any DOM node, which caused breakage when I originally
attempted to use a <content> tag to bring in the header or
group title content into gr-change-list-item.
+ The flexibility of flexbox allows us to style the change list
much easier on smaller screens, so it was probably going to
happen anyway.
+ Full-width (colspan="<total number of columns in the table>")
rows for the headers is much more difficult when using elements
outside of the gr-change-list-item brought in via <content> as
described above.
+ gr-change-list-item was doing too much anyway.
Feature: Issue 3700
Change-Id: I6536bf7d18adfa460507f8050a15d83e84af82a7
7aa52d3d0a