Change Ia3a97599f8 refactored FileInfoJson to have two implementations:
the current one, and another using the new diff cache redesign. The
previous refactoring also modified FilesInCommitCollection to use the
new FileInfoJson API.
The previous implementation allowed passing a value '0' for parentNum to
FilesInCommitCollection, which was not handled in this refactoring. This
change fixes this case in FileInfoJsonOldImpl and adds tests for
FilesInCommitCollection.
Passing a value '0' was not mentioned in the docs, although it was
handled in the code. I modified the docs to include this case.
Change-Id: I65d505e574acbaf64c68f5cc7ec622ae3f2ab923
8df6d5c36b