Update getFileWebLink signature to match Gerrit

Gerrit is getting a new getFileWebLink method signature in order to
support additional gitweb alternatives like gitea. Gitiles needs to
update its overridden method to match the new signature.

Depends-On: https://gerrit-review.googlesource.com/c/gerrit/+/329279
Change-Id: I9b0e73504245e22cf5ad1b0075ca8a972d0a703e