Unknown WebAXRole from Blink should be mapped to a valid chromium AX role.

Unknown WebAXRole from Blink should be mapped to a valid chromium AX role.

If not, it leads to a crash later because we don't expect invalied AX roles
in Chromium. We have to tolerate unknown AX roles from Blink because
otherwise there's no way for us to introduce new roles to the Blink enum.

BUG=426608
TBR=aboxhall

Committed: https://crrev.com/6874f8183601e89123e52b636cf49777dc40d7f1
Cr-Commit-Position: refs/heads/master@{#301072}

[dmazzoni, 2014-10-24 06:58:48]

dmazzoni@chromium.org changed reviewers:
+ aboxhall@chromium.org

[dmazzoni, 2014-10-24 06:58:51]

The CQ bit was checked by dmazzoni@chromium.org

[commit-bot: I haz the power, 2014-10-24 06:59:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/673143002/1

[commit-bot: I haz the power, 2014-10-24 07:47:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-24 07:48:37]

Patchset 1 (id:??) landed as
https://crrev.com/6874f8183601e89123e52b636cf49777dc40d7f1
Cr-Commit-Position: refs/heads/master@{#301072}