Add log output if a download triggered by a page redirects cross-origin

The next step will be to figure out how to get back to the initiating
WebContents, dump the redirect chain into a LoadURLParams struct,
and continue the download as navigation.

BUG=831073
[email protected],[email protected]

Change-Id: I28c55fdc9982433b684184b234f8f503c46facc5
Reviewed-on: https://chromium-review.googlesource.com/1135307
Reviewed-by: Min Qin <[email protected]>
Reviewed-by: Mike West <[email protected]>
Commit-Queue: Jochen Eisinger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#574890}
26 files changed