Stop building FilePathWatcher on iOS.

Stop building FilePathWatcher on iOS.

Stop using FilePathWatcher on iOS as it does not works on iOS devices
as can be seen when running the unit tests that never finish as no
events are reported.

Remove the only usage of FilePathWatcher that was present on iOS. This
does not change the behaviour since previously even in case of changes
to /etc/hosts, the watcher was never informed of any changes. Moreover
the file is not editable by the user and so the file will only change
after OS upgrade (which requires an app restart) or due to a list of
static hosts send as part of dynamic IP negociation (i.e. after a local
IP change).

BUG=477102
Committed: https://crrev.com/d8143e7373719ed53b6cef35c234b0498b771d48
Cr-Commit-Position: refs/heads/master@{#348400}

[sdefresne, 2015-09-10 10:14:14]

sdefresne@chromium.org changed reviewers:
+ rvargas@chromium.org

[sdefresne, 2015-09-10 10:14:15]

rvargas: can you please take a look?

[rvargas (doing something else), 2015-09-10 19:07:11]

lgtm

[sdefresne, 2015-09-11 13:05:46]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-09-11 13:06:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1304233004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1304233004/1

[commit-bot: I haz the power, 2015-09-11 15:16:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-11 15:17:51]

Patchset 1 (id:??) landed as
https://crrev.com/d8143e7373719ed53b6cef35c234b0498b771d48
Cr-Commit-Position: refs/heads/master@{#348400}

[commit-bot: I haz the power, 2015-09-23 12:22:33]

Patchset 1 (id:??) landed as
https://crrev.com/d8143e7373719ed53b6cef35c234b0498b771d48
Cr-Commit-Position: refs/heads/master@{#348400}