Fix and reenable liblouis chromevox tests.

Address flake in the liblouis wrapper.

This fixes and reenables liblouis chromevox tests.  Instead of relying on
the 'load' event of the nacl component, just queue up requests to
the component as soon as it is attached.  This simplifies the state management
in the wrapper.

As a bonus, the tests are fixed to use the appropriate callback
wrappers so that errors are immediately reported in failure cases
instead of making the tests painfully block and time out.

BUG=458910
Committed: https://crrev.com/eff7d2454cc5eff276b0a3e64da1219aead6b5d8
Cr-Commit-Position: refs/heads/master@{#316658}

[Peter Lundblad, 2015-02-17 16:39:00]

plundblad@chromium.org changed reviewers:
+ dtseng@chromium.org

[David Tseng, 2015-02-17 20:00:13]

lgtm

[Peter Lundblad, 2015-02-17 20:40:55]

New patchsets have been uploaded after l-g-t-m from dtseng@chromium.org

[Peter Lundblad, 2015-02-17 21:12:54]

The CQ bit was checked by plundblad@chromium.org

[commit-bot: I haz the power, 2015-02-17 21:14:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/927313002/60001

[commit-bot: I haz the power, 2015-02-17 21:39:45]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-02-17 21:40:44]

Patchset 4 (id:??) landed as
https://crrev.com/eff7d2454cc5eff276b0a3e64da1219aead6b5d8
Cr-Commit-Position: refs/heads/master@{#316658}