Implement disabled list

Implement disabled list

To promote using the original tab as the primary download source
for a page, we are making changes to disable a page for background
downloading until the foreground is done. This part of the larger
change implements the disabled list.

BUG=652889
Review-Url: https://codereview.chromium.org/2395213002
Cr-Commit-Position: refs/heads/master@{#424226}
(cherry picked from commit f75ba66f9a4b29bc62d2716b3a2816cc69b8b271)

Committed: https://chromium.googlesource.com/chromium/src/+/ee359f2511345003cb17ba84f02ba788b9dae758

[Pete Williamson, 2016-10-11 23:12:41]

Description was changed from

==========
Implement disabled list

To promote using the original tab as the primary download source
for a page, we are making changes to disable a page for background
downloading until the foreground is done. This part of the larger
change implements the disabled list.

BUG=652889

Review-Url: https://codereview.chromium.org/2395213002
Cr-Commit-Position: refs/heads/master@{#424226}
(cherry picked from commit f75ba66f9a4b29bc62d2716b3a2816cc69b8b271)
==========

to

==========
Implement disabled list

To promote using the original tab as the primary download source
for a page, we are making changes to disable a page for background
downloading until the foreground is done. This part of the larger
change implements the disabled list.

BUG=652889

Review-Url: https://codereview.chromium.org/2395213002
Cr-Commit-Position: refs/heads/master@{#424226}
(cherry picked from commit f75ba66f9a4b29bc62d2716b3a2816cc69b8b271)

Committed:
https://chromium.googlesource.com/chromium/src/+/ee359f2511345003cb17ba84f02b...
==========

[Pete Williamson, 2016-10-11 23:12:44]

Committed patchset #1 (id:1) manually as
ee359f2511345003cb17ba84f02ba788b9dae758.