GN: Throw an error for duplicate object files.

GN: Throw an error for duplicate object files.

Detect duplicate object files in the same target and throw an error. This provides a stronger barrier and a more actionable message than the Ninja "multiple rules" error that will result.

Committed: https://crrev.com/874d7ad541925ea79c94d9a8000407c7d5bb2c91
Cr-Commit-Position: refs/heads/master@{#336853}

[brettw, 2015-06-30 17:47:44]

brettw@chromium.org changed reviewers:
+ thakis@chromium.org

[brettw, 2015-06-30 17:47:45]

As per your request.

[brettw, 2015-06-30 17:47:49]

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

[commit-bot: I haz the power, 2015-06-30 17:50:11]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1210143003/20001

[commit-bot: I haz the power, 2015-06-30 18:09:02]

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

[commit-bot: I haz the power, 2015-06-30 18:09:03]

Dry run: This issue passed the CQ dry run.

[Nico, 2015-06-30 18:19:06]

lgtm, thanks!

(no test?)

[tfarina, 2015-06-30 18:47:42]

tfarina@chromium.org changed reviewers:
+ tfarina@chromium.org

[tfarina, 2015-06-30 18:47:42]

This is nice and clean.

lgtm2.

[brettw, 2015-06-30 19:14:15]

On 2015/06/30 18:19:06, Nico wrote:
> lgtm, thanks!
> 
> (no test?)

I went back and forth on whether a test would be useful. But now you've made me
feel guilty so I added one. It was shorter than I feared.

[brettw, 2015-06-30 19:14:33]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-06-30 19:14:34]

The patchset sent to the CQ was uploaded after l-g-t-m from thakis@chromium.org
Link to the patchset: https://codereview.chromium.org/1210143003/#ps40001
(title: "test")

[commit-bot: I haz the power, 2015-06-30 19:17:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1210143003/40001

[commit-bot: I haz the power, 2015-06-30 19:32:15]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-06-30 19:33:13]

Patchset 3 (id:??) landed as
https://crrev.com/874d7ad541925ea79c94d9a8000407c7d5bb2c91
Cr-Commit-Position: refs/heads/master@{#336853}