Drop the suggested name of downloads when initiator & resource origin differ

Compare https://html.spec.whatwg.org/#downloading-resources step 3-9.

BUG=714373
R=dtrainor@chromium.org

Change-Id: Iae9831c488fac56442ebf608203853da022fdf10
Reviewed-on: https://chromium-review.googlesource.com/509253
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#473428}
4 files changed