[Autofill] Split TestAutofillDownloadManager logic out of MockAutofillDownloadManager

Bug: 778436
Change-Id: Iec4eb44ae35f53952bd51785140851b32add4a12
Reviewed-on: https://chromium-review.googlesource.com/852989
Commit-Queue: Sebastien Seguin-Gagnon <[email protected]>
Reviewed-by: Sebastien Seguin-Gagnon <[email protected]>
Cr-Commit-Position: refs/heads/master@{#527633}
4 files changed