Remove usage of base::ObserverList<T>::Iter::GetNext() in //components/prefs.

Remove usage of base::ObserverList<T>::Iter::GetNext() in //components/prefs.

Observer lists now support range-based for loops.

BUG=655021
Committed: https://crrev.com/018341c1b436b105874d589bbc1b0c8b6a8a1f9e
Cr-Commit-Position: refs/heads/master@{#425480}

[dcheng, 2016-10-12 23:25:03]

The CQ bit was checked by dcheng@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-12 23:25:32]

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

[dcheng, 2016-10-12 23:29:12]

dcheng@chromium.org changed reviewers:
+ pam@chromium.org

[commit-bot: I haz the power, 2016-10-13 00:42:30]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-13 00:42:31]

Dry run: This issue passed the CQ dry run.

[Pam (message me for reviews), 2016-10-14 20:35:26]

https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
File components/prefs/pref_notifier_impl.cc (right):

https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
components/prefs/pref_notifier_impl.cc:22: if (observer_list.second->begin() !=
observer_list.second->end())
Why not observer_list.second->size() ?

[dcheng, 2016-10-14 20:38:40]

https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
File components/prefs/pref_notifier_impl.cc (right):

https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
components/prefs/pref_notifier_impl.cc:22: if (observer_list.second->begin() !=
observer_list.second->end())
On 2016/10/14 20:35:26, Pam (message me for reviews) wrote:
> Why not observer_list.second->size() ?

size() isn't exposed by ObserverList. Since ObserverList is thread-safe-ish,
allow reentrancy, and allows mutation of ObserverList while dispatching to
observers, it turns out to be a bit tricky to implement this in a performant
way.

Thus, this somewhat silly looking check.

[Pam (message me for reviews), 2016-10-14 20:42:19]

On 2016/10/14 20:38:40, dcheng wrote:
>
https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
> File components/prefs/pref_notifier_impl.cc (right):
> 
>
https://codereview.chromium.org/2415793002/diff/1/components/prefs/pref_notif...
> components/prefs/pref_notifier_impl.cc:22: if (observer_list.second->begin()
!=
> observer_list.second->end())
> On 2016/10/14 20:35:26, Pam (message me for reviews) wrote:
> > Why not observer_list.second->size() ?
> 
> size() isn't exposed by ObserverList. Since ObserverList is thread-safe-ish,
> allow reentrancy, and allows mutation of ObserverList while dispatching to
> observers, it turns out to be a bit tricky to implement this in a performant
> way.
> 
> Thus, this somewhat silly looking check.

Ah, makes sense. LGTM; thanks for the cleanup!

[dcheng, 2016-10-14 20:43:38]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2016-10-14 20:44:14]

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, 2016-10-14 21:54:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-14 21:55:54]

Description was changed from

==========
Remove usage of base::ObserverList<T>::Iter::GetNext() in //components/prefs.

Observer lists now support range-based for loops.

BUG=655021
==========

to

==========
Remove usage of base::ObserverList<T>::Iter::GetNext() in //components/prefs.

Observer lists now support range-based for loops.

BUG=655021

Committed: https://crrev.com/018341c1b436b105874d589bbc1b0c8b6a8a1f9e
Cr-Commit-Position: refs/heads/master@{#425480}
==========

[commit-bot: I haz the power, 2016-10-14 21:55:55]

Patchset 1 (id:??) landed as
https://crrev.com/018341c1b436b105874d589bbc1b0c8b6a8a1f9e
Cr-Commit-Position: refs/heads/master@{#425480}