Adjust the visibility of the standalone targets in the GN build.

Adjust the visibility of the standalone targets in the GN build.

As part of the migration from GYP->GN, we want to make sure that we
can track when new targets are added to either the GYP or GN builds
and that we are building everything we expect to build.

In GN, unlike GYP, if a build file gets referenced from other files,
building 'all' will cause every target to be built in it. This means in
particular, that we can end up trying to build targets that are not
necessarily intended to be visible to the rest of the build. To get
around this, any target that is defined but hidden (like 'v8_snapshot',
in V8's case) should still be visible to a top-level target called
"//:gn_visibility".

R=brettw@chromium.org, machenbach@chromium.org
BUG=461019
LOG=N

Committed: https://crrev.com/978acb8d5eff56d924fef6af63582ccf2497b437
Cr-Commit-Position: refs/heads/master@{#28243}

[Dirk Pranke, 2015-05-01 20:59:46]

Patchset #1 (id:1) has been deleted

[Michael Achenbach, 2015-05-04 15:26:35]

lgtm

[Dirk Pranke, 2015-05-05 19:43:44]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-05-05 19:44:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1120093005/20001

[commit-bot: I haz the power, 2015-05-05 19:47:48]

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

[commit-bot: I haz the power, 2015-05-05 19:47:49]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/2471)

[Dirk Pranke, 2015-05-05 19:48:50]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-05-05 19:49:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1120093005/20001

[commit-bot: I haz the power, 2015-05-05 21:16:25]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-05-05 21:16:38]

Patchset 1 (id:??) landed as
https://crrev.com/978acb8d5eff56d924fef6af63582ccf2497b437
Cr-Commit-Position: refs/heads/master@{#28243}