Add missing BASE_EXPORT to LogErrorNotReached().

Add missing BASE_EXPORT to LogErrorNotReached().

This fixes a linker error that was introduced in
https://codereview.chromium.org/1124673004/.

BUG=484283
TBR=danakj@chromium.org

Committed: https://crrev.com/80388e68135256245a4f44b4c161136cf5580847
Cr-Commit-Position: refs/heads/master@{#331354}

[Thiemo Nagel, 2015-05-26 09:03:23]

The CQ bit was checked by tnagel@chromium.org

[commit-bot: I haz the power, 2015-05-26 09:04:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1155163002/1

[commit-bot: I haz the power, 2015-05-26 11:22:51]

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

[commit-bot: I haz the power, 2015-05-26 11:22:52]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[Thiemo Nagel, 2015-05-26 11:29:30]

The CQ bit was checked by tnagel@chromium.org

[Thiemo Nagel, 2015-05-26 11:29:57]

On 2015/05/26 11:22:52, I haz the power - commit-bot wrote:
> Try jobs failed on following builders:
>   mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

Assuming flake.  Retrying.

[commit-bot: I haz the power, 2015-05-26 11:30:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1155163002/1

[commit-bot: I haz the power, 2015-05-26 13:28:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-26 13:29:04]

Patchset 1 (id:??) landed as
https://crrev.com/80388e68135256245a4f44b4c161136cf5580847
Cr-Commit-Position: refs/heads/master@{#331354}

[Thiemo Nagel, 2016-03-24 10:40:57]

Patchset #2 (id:20001) has been deleted