Add GN win x64 bots to buildbot/testing/chromium.win.json.

Add GN win x64 bots to buildbot/testing/chromium.win.json.

This makes the new trybots actually build the same targets
as the waterfall bots, rather than 'all' (which doesn't
work at the moment).

TBR=phajdan.jr@chromium.org
BUG=477879
Committed: https://crrev.com/8a49dea48cf41f30a1ff6d5af90349822169ba6c
Cr-Commit-Position: refs/heads/master@{#326979}

[Dirk Pranke, 2015-04-25 18:01:53]

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

[commit-bot: I haz the power, 2015-04-25 18:01:58]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1078983006/1

[commit-bot: I haz the power, 2015-04-25 19:16:33]

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

[commit-bot: I haz the power, 2015-04-25 19:16:34]

Dry run: This issue passed the CQ dry run.

[Dirk Pranke, 2015-04-25 21:53:29]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-04-25 21:53:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1078983006/1

[commit-bot: I haz the power, 2015-04-25 21:54:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-25 21:54:51]

Patchset 1 (id:??) landed as
https://crrev.com/8a49dea48cf41f30a1ff6d5af90349822169ba6c
Cr-Commit-Position: refs/heads/master@{#326979}