Fix typo in js code when checking the origin of a message coming from the

Fix typo in js code when checking the origin of a message coming from the
embedded webview.  The length of the string was not correctly calculated.

BUG=None

Committed: https://crrev.com/238a196c42ae644171f96697a828a11d6478f178
Cr-Commit-Position: refs/heads/master@{#311488}

[Roger Tawa OOO till Jul 10th, 2015-01-13 19:42:19]

rogerta@chromium.org changed reviewers:
+ xiyuan@chromium.org

[Roger Tawa OOO till Jul 10th, 2015-01-13 19:42:20]

Hi Xiyuan,

Can you review this typo in the js authenticator code?  I found this while
trying to test password handling on staging.

[xiyuan, 2015-01-13 20:17:29]

lgtm

[Roger Tawa OOO till Jul 10th, 2015-01-14 00:13:21]

The CQ bit was checked by rogerta@chromium.org

[commit-bot: I haz the power, 2015-01-14 00:14:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/848943003/1

[commit-bot: I haz the power, 2015-01-14 00:29:10]

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

[commit-bot: I haz the power, 2015-01-14 00:29:11]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)

[Roger Tawa OOO till Jul 10th, 2015-01-14 16:25:39]

The CQ bit was checked by rogerta@chromium.org

[commit-bot: I haz the power, 2015-01-14 16:26:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/848943003/20001

[commit-bot: I haz the power, 2015-01-14 16:30:29]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-14 16:31:47]

Patchset 2 (id:??) landed as
https://crrev.com/238a196c42ae644171f96697a828a11d6478f178
Cr-Commit-Position: refs/heads/master@{#311488}