The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a816bfc268006458526fb07e84ac1e03cd1ac03f

commit a816bfc268006458526fb07e84ac1e03cd1ac03f
Author: skym <skym@chromium.org>
Date: Tue Nov 15 18:57:05 2016

[Sync] Return nullptr for OpenTabsUIDelegate when PROXY_TABS is disabled.

Previously each UI component that relied on this would have its separate checks to see if PROXY_TABS was enabled or not, and only display the tabs data from the OpenTabsUIDelegate if it was. As more UI was created that relied on foreign tabs data, we saw the mistake of not making this check occur multiple times.

This change will result in a null OpenTabsUIDelegate being provided when proxy tabs is disabled, and it will be impossible to make the mentioned mistake.

Going forward, there are a handful of places with logic that checks and/or passes around if proxy tabs is enabled or not. As a follow up to this CL, we should go through and remove/simplify all that logic as foreign tabs data will no longer be accessible when proxy tabs becomes disabled.

BUG= 662601 

Review-Url: https://codereview.chromium.org/2504433002
Cr-Commit-Position: refs/heads/master@{#432227}

[modify] https://crrev.com/a816bfc268006458526fb07e84ac1e03cd1ac03f/chrome/browser/extensions/api/sessions/sessions_apitest.cc
[modify] https://crrev.com/a816bfc268006458526fb07e84ac1e03cd1ac03f/components/browser_sync/profile_sync_service.cc
[modify] https://crrev.com/a816bfc268006458526fb07e84ac1e03cd1ac03f/components/browser_sync/profile_sync_service_unittest.cc
[modify] https://crrev.com/a816bfc268006458526fb07e84ac1e03cd1ac03f/components/sync/driver/sync_service.h