Fix GN visibility for a few targets that are compiled by default in a GN build.

Fix GN visibility for a few targets that are compiled by default in a GN build.

When we build 'all' in GN, we can end up building targets that are
defined in various build files even if they are not transitively referenced
from 'gn_all' or 'gn_only'. This is undesirable because it makes it harder
to tell when there might be discrepancies between the GN and GYP builds.

Some of these targets may actually be hidden (using the visibility tag)
and only intended to be depended on by other targets that don't work yet.
By making this targets also visible to a top-level "//:gn_visibility"
target we can ensure that we're tracking them properly without breaking
the normal encapsulation rules.

The two targets affected in this patch are
- //build/config/sanitizers:options_sources
- //ui/resources:repack_ui_test_mac_locale_pack

R=brettw@chromium.org
BUG=431177
CQ_EXTRA_TRYBOTS=tryserver.chromium.mac:mac_chromium_gn_rel,mac_chromium_gn_dbg

Committed: https://crrev.com/b6128d057b09ade62d23528b6f919d5007f9defc
Cr-Commit-Position: refs/heads/master@{#327922}

[Dirk Pranke, 2015-05-01 01:00:25]

Brett, are you okay with this approach? These two targets are trivially
unimportant, but there are targets that do matter in pdfium and v8 that I would
like to be able to account for this way.

[Dirk Pranke, 2015-05-01 01:18:44]

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

[commit-bot: I haz the power, 2015-05-01 01:19:42]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1121453004/20001

[commit-bot: I haz the power, 2015-05-01 01:45:25]

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

[commit-bot: I haz the power, 2015-05-01 01:45:25]

Dry run: This issue passed the CQ dry run.

[brettw, 2015-05-01 16:38:08]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-05-01 16:38:08]

lgtm

[commit-bot: I haz the power, 2015-05-01 16:39:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1121453004/20001

[commit-bot: I haz the power, 2015-05-01 16:40:41]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-01 16:41:54]

Patchset 2 (id:??) landed as
https://crrev.com/b6128d057b09ade62d23528b6f919d5007f9defc
Cr-Commit-Position: refs/heads/master@{#327922}