Fix MB configs for chromium.webkit Android GN bots.

Fix MB configs for chromium.webkit Android GN bots.

... which weren't specifying android builds :).

R=phajdan.jr@chromium.org
BUG=454413
Committed: https://crrev.com/6ae2d0ad19bfe63d071d5dd24240e3b5cc7273ca
Cr-Commit-Position: refs/heads/master@{#325559}

[Dirk Pranke, 2015-04-16 20:43:06]

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

[commit-bot: I haz the power, 2015-04-16 20:44:46]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1090053002/1

[Paweł Hajdan Jr., 2015-04-16 21:33:44]

LGTM

[commit-bot: I haz the power, 2015-04-16 23:57:18]

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

[commit-bot: I haz the power, 2015-04-16 23:57:21]

Dry run: This issue passed the CQ dry run.

[Dirk Pranke, 2015-04-16 23:58:58]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-04-16 23:59:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1090053002/1

[commit-bot: I haz the power, 2015-04-17 00:02:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-17 00:02:47]

Patchset 1 (id:??) landed as
https://crrev.com/6ae2d0ad19bfe63d071d5dd24240e3b5cc7273ca
Cr-Commit-Position: refs/heads/master@{#325559}