Revert of Cross-process iframe accessibility.

Revert of Cross-process iframe accessibility. (patchset #19 id:360001 of https://codereview.chromium.org/268543008/)

Reason for revert:
Broke Mac tests:

http://build.chromium.org/p/chromium.mac/builders/Mac10.7%20Tests%20%281%29/builds/26131

http://build.chromium.org/p/chromium.mac/builders/Mac%2010.6%20Tests%20%28dbg%29%281%29/builds/52684

http://build.chromium.org/p/chromium.mac/builders/Mac%2010.7%20Tests%20%28dbg%29%281%29/builds/26975

http://build.chromium.org/p/chromium.mac/builders/Mac%2010.7%20Tests%20%28dbg%29%281%29/builds/26976

and so on.

Original issue's description:
> Cross-process iframe accessibility.
> 
> This change completes the plumbing to join cross-process iframes into a single composed accessibility tree on platforms that implement native accessibility APIs (Windows, Mac, Android).
> 
> Further work will be needed to update some accessibility API implementations to be multi-frame-aware.
> 
> BUG=368298
> 
> Committed: https://crrev.com/387942c041da17ea6337bc0a81e96619e67e4ac4
> Cr-Commit-Position: refs/heads/master@{#294118}

TBR=creis@chromium.org,dtseng@chromium.org,aboxhall@chromium.org,nick@chromium.org,nasko@chromium.org,dmazzoni@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=368298
Committed: https://crrev.com/1dcb3ab78bde4c56037d79ac58d73fb2fca8a39b
Cr-Commit-Position: refs/heads/master@{#294135}

[dconnelly, 2014-09-10 07:42:44]

Created Revert of Cross-process iframe accessibility.

[commit-bot: I haz the power, 2014-09-10 07:43:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dconnelly@chromium.org/558943002/1

[commit-bot: I haz the power, 2014-09-10 07:45:16]

Committed patchset #1 (id:1) as 77ca0cd16e0d78887e053f067cd8c5a3207f5f1e

[commit-bot: I haz the power, 2014-09-10 07:52:31]

Patchset 1 (id:??) landed as
https://crrev.com/1dcb3ab78bde4c56037d79ac58d73fb2fca8a39b
Cr-Commit-Position: refs/heads/master@{#294135}