remove dead code: AddPageToDownloadManagerTask

Change-Id: Ieaf2be762ed4719a7404c6b51c56db10fc367afa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574978
Reviewed-by: Peter Williamson <petewil@chromium.org>
Commit-Queue: Dan H <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652406}
4 files changed