Implement MarkRequestCompleted.

Implement MarkRequestCompleted.

When the foreground tab finishes a request, it will let us know, and we
need to send out the observer notification.  This code catches the
foreground request completing, and calls the observer with SUCCESS
after removing the request, and starting the next available request.

BUG=652889
Review-Url: https://codereview.chromium.org/2409823002
Cr-Commit-Position: refs/heads/master@{#424346}
(cherry picked from commit b1c4cc221dd01af09ceaf1eba05735046bd46d0b)

Committed: https://chromium.googlesource.com/chromium/src/+/b6d6eaef2b28bbfa7cc0be5ab099cdaf0570f2c9

[Pete Williamson, 2016-10-11 23:24:28]

Description was changed from

==========
Implement MarkRequestCompleted.

When the foreground tab finishes a request, it will let us know, and we
need to send out the observer notification.  This code catches the
foreground request completing, and calls the observer with SUCCESS
after removing the request, and starting the next available request.

BUG=652889

Review-Url: https://codereview.chromium.org/2409823002
Cr-Commit-Position: refs/heads/master@{#424346}
(cherry picked from commit b1c4cc221dd01af09ceaf1eba05735046bd46d0b)
==========

to

==========
Implement MarkRequestCompleted.

When the foreground tab finishes a request, it will let us know, and we
need to send out the observer notification.  This code catches the
foreground request completing, and calls the observer with SUCCESS
after removing the request, and starting the next available request.

BUG=652889

Review-Url: https://codereview.chromium.org/2409823002
Cr-Commit-Position: refs/heads/master@{#424346}
(cherry picked from commit b1c4cc221dd01af09ceaf1eba05735046bd46d0b)

Committed:
https://chromium.googlesource.com/chromium/src/+/b6d6eaef2b28bbfa7cc0be5ab099...
==========

[Pete Williamson, 2016-10-11 23:24:31]

Committed patchset #1 (id:1) manually as
b6d6eaef2b28bbfa7cc0be5ab099cdaf0570f2c9.