ntp_tiles: Fix Top Sites potentially overriding Suggestions Service

ntp_tiles: Fix Top Sites potentially overriding Suggestions Service

The current implementation of MostVisitedSites has a race condition
which can cause Top Sites tiles to be shown in the NTP although
Suggestions Service results are available.

As reflected in updated tests, this is the case when Top Sites takes
longer to respond than the Suggestions Service, but only if no cached
tiles exist for the Suggestions Service.

BUG=674909
Review-Url: https://codereview.chromium.org/2584853002
Cr-Commit-Position: refs/heads/master@{#441632}
Committed: https://chromium.googlesource.com/chromium/src/+/648408687025e4e954a392135c93e80a43481b10

[mastiz, 2016-12-16 13:54:58]

mastiz@chromium.org changed reviewers:
+ sfiera@chromium.org

[sfiera, 2016-12-16 14:46:40]

LGTM

[mastiz, 2017-01-05 11:46:37]

The CQ bit was checked by mastiz@chromium.org

[mastiz, 2017-01-05 11:46:37]

The patchset sent to the CQ was uploaded after l-g-t-m from sfiera@chromium.org
Link to the patchset: https://codereview.chromium.org/2584853002/#ps20001
(title: "Rebased.")

[commit-bot: I haz the power, 2017-01-05 11:46:55]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-05 12:42:36]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1483616797176360,
"parent_rev": "566236e262e49531224e263885e6208259725ab0", "commit_rev":
"648408687025e4e954a392135c93e80a43481b10"}

[commit-bot: I haz the power, 2017-01-05 12:43:06]

Description was changed from

==========
ntp_tiles: Fix Top Sites potentially overriding Suggestions Service

The current implementation of MostVisitedSites has a race condition
which can cause Top Sites tiles to be shown in the NTP although
Suggestions Service results are available.

As reflected in updated tests, this is the case when Top Sites takes
longer to respond than the Suggestions Service, but only if no cached
tiles exist for the Suggestions Service.

BUG=674909
==========

to

==========
ntp_tiles: Fix Top Sites potentially overriding Suggestions Service

The current implementation of MostVisitedSites has a race condition
which can cause Top Sites tiles to be shown in the NTP although
Suggestions Service results are available.

As reflected in updated tests, this is the case when Top Sites takes
longer to respond than the Suggestions Service, but only if no cached
tiles exist for the Suggestions Service.

BUG=674909

Review-Url: https://codereview.chromium.org/2584853002
Cr-Commit-Position: refs/heads/master@{#441632}
Committed:
https://chromium.googlesource.com/chromium/src/+/648408687025e4e954a392135c93...
==========

[commit-bot: I haz the power, 2017-01-05 12:43:07]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/648408687025e4e954a392135c93...