Disable dev channel crashes for Extension JS exceptions.

Disable dev channel crashes for Extension JS exceptions.

This is a temporary patch so that the next dev release branch won't have high
crash rates due to this bug. The crash is explicitly disabled on stable and
beta branches anyway. Once dev next branches, this will be reverted as we
return to trying to fix it.

BUG=471599
R=yoz@chromium.org

Committed: https://crrev.com/d774155ed89969a8181932f9f2db8ebc179f5b5e
Cr-Commit-Position: refs/heads/master@{#323841}

[Yoyo Zhou, 2015-04-03 20:18:56]

LGTM, seems legit.

[not at google - send to devlin, 2015-04-03 21:33:45]

The CQ bit was checked by kalman@chromium.org

[commit-bot: I haz the power, 2015-04-03 21:34:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1059383002/1

[commit-bot: I haz the power, 2015-04-03 22:50:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-03 22:54:00]

Patchset 1 (id:??) landed as
https://crrev.com/d774155ed89969a8181932f9f2db8ebc179f5b5e
Cr-Commit-Position: refs/heads/master@{#323841}