Prevent landmines.py from deleting your source directory.

Prevent landmines.py from deleting your source directory.

Previously, if CHROMIUM_OUT_DIR was set but blank, it could (and did!)
delete your entire source directory, including .git folder.

BUG=446921
Committed: https://crrev.com/89d303ac3e23adf4ecff08e459a6bdf6b81ff033
Cr-Commit-Position: refs/heads/master@{#311326}

[johnme, 2015-01-07 18:46:28]

johnme@chromium.org changed reviewers:
+ scottmg@chromium.org

[scottmg, 2015-01-07 19:48:19]

How did you end up with an empty variable? I think I would prefer an abort here
to encourage fixing it, rather than a print to stderr.

[johnme, 2015-01-07 20:28:41]

On 2015/01/07 19:48:19, scottmg wrote:
> How did you end up with an empty variable?

I had a Bash function which ran:

$ export CHROMIUM_OUT_DIR=$(cr info -s CR_OUT_BASE)

But for whatever reason the call to cr failed (wasn't found perhaps), and so
this evaluated to the empty string.

> I think I would prefer an abort here
> to encourage fixing it, rather than a print to stderr.

Done.

[scottmg, 2015-01-13 20:28:34]

lgtm

[johnme, 2015-01-13 20:32:19]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2015-01-13 20:33:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/832933004/20001

[commit-bot: I haz the power, 2015-01-13 21:29:09]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-13 21:30:08]

Patchset 2 (id:??) landed as
https://crrev.com/89d303ac3e23adf4ecff08e459a6bdf6b81ff033
Cr-Commit-Position: refs/heads/master@{#311326}