Fix NaCl IRT copy in GN chrome build.

Fix NaCl IRT copy in GN chrome build.

When we build the IRT in GN, it gets built into
out/*/irt_x64/nacl_irt.nexe, but it needs to be copied
to out/*/nacl_irt_x86_64.nexe.

There were two places in the GN build that depended on
the IRT; the chrome dependency only depended on the toolchain-specific
location, and the browser_tests dependency only worked if
the nacl browsertests are enabled (which they currently aren't,
by default).

As a result, we may not get the IRT build into the right
location, and the 'nacl_integration' build step might fail (though
it might succeed if it happened to find an old binary lying around).

Fixing the chrome dependency should cause the nacl_integration
step to pass again.

TBR=jam@chromium.org, phosek@chromium.org, brettw@chromium.org
BUG=529988
Committed: https://crrev.com/4ba62625fd00601ce4e806f8e1bacdda893bf24d
Cr-Commit-Position: refs/heads/master@{#348226}

[Dirk Pranke, 2015-09-10 20:01:54]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-09-10 20:02:28]

dpranke@chromium.org changed reviewers:
+ brettw@chromium.org, phosek@chromium.org

[commit-bot: I haz the power, 2015-09-10 20:03:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338453002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338453002/1

[jam, 2015-09-10 20:09:35]

rubberstamp lgtm

[commit-bot: I haz the power, 2015-09-10 20:49:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-10 20:50:05]

Patchset 1 (id:??) landed as
https://crrev.com/4ba62625fd00601ce4e806f8e1bacdda893bf24d
Cr-Commit-Position: refs/heads/master@{#348226}

[commit-bot: I haz the power, 2015-09-23 12:13:52]

Patchset 1 (id:??) landed as
https://crrev.com/4ba62625fd00601ce4e806f8e1bacdda893bf24d
Cr-Commit-Position: refs/heads/master@{#348226}