Mark class as exported to fix win build.

Mark class as exported to fix win build.

TBR=machenbach@chromium.org
BUG=chromium:470930
LOG=N

Committed: https://crrev.com/dea59184cc44ac131c43596972bea49524dae85e
Cr-Commit-Position: refs/heads/master@{#28647}

[vogelheim, 2015-05-27 06:44:26]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-05-27 06:44:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1149923006/1

[commit-bot: I haz the power, 2015-05-27 06:47:44]

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

[commit-bot: I haz the power, 2015-05-27 06:47:45]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/2985)

[vogelheim, 2015-05-27 07:03:26]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-05-27 07:03:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1149923006/1

[Michael Achenbach, 2015-05-27 07:08:49]

lgtm

[commit-bot: I haz the power, 2015-05-27 07:10:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-27 07:10:56]

Patchset 1 (id:??) landed as
https://crrev.com/dea59184cc44ac131c43596972bea49524dae85e
Cr-Commit-Position: refs/heads/master@{#28647}