Changes with large numbers of files could overwhelm PolyGerrit when a
user selects [Expand all] for inline diffs. This was because the
asynchronous processing/rendering/annotating process would be kicked off
for all unexpanded diffs simultaneously, resulting in browser lock-up
and general slowness even after rendering had completed.
With this change, inline diffs are rendered in serial rather than
parallel. In this way the benefits of the async features of diff
rendering extend to the file list, even for changes with many large
diffs (such as the one in the linked issue).
With this change, the `__expanded` property is removed from file objects
in GR-FILE-LIST. Instead, that element maintains a list
(`_expandedFilePaths`) which records the same information. Because the
expanded files are recorded in a list, however, splices on the list can
be observed, batch diff expansion can be handled sequentially.
Tests are updated to respect the new expanded paths list.
Bug: Issue 5396
Change-Id: Ib83ff5157177e1c890db8a82fbc25df8fecbe065
206966a5ae