Add AX role conversions for EmbedObject, Figcaption and Figure for test_runner

Add conversions for EmbedObject, Figcaption and Figure
at Web_ax_object_proxy.cc It's for Blink test_runner.

BUG=N/A

Committed: https://crrev.com/aa5362514e13e46823d1b1e128fd1376c6d656b4
Cr-Commit-Position: refs/heads/master@{#296732}

[je_julie(Not used), 2014-09-25 07:03:47]

je_julie.kim@samsung.com changed reviewers:
+ dmazzoni@chromium.org

[je_julie(Not used), 2014-09-25 07:05:01]

Dominic, PTAL.

[dmazzoni, 2014-09-25 16:43:05]

The CQ bit was checked by dmazzoni@chromium.org

[dmazzoni, 2014-09-25 16:43:05]

lgtm

[commit-bot: I haz the power, 2014-09-25 16:43:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/599363002/1

[commit-bot: I haz the power, 2014-09-25 17:23:43]

Committed patchset #1 (id:1) as a045fcc4daa128e207698bafa2fe52f258224513

[commit-bot: I haz the power, 2014-09-25 17:24:20]

Patchset 1 (id:??) landed as
https://crrev.com/aa5362514e13e46823d1b1e128fd1376c6d656b4
Cr-Commit-Position: refs/heads/master@{#296732}