Revert of Fix accessibility with out-of-process iframes.

Revert of Fix accessibility with out-of-process iframes. (patchset #12 id:220001 of https://codereview.chromium.org/1155993003/)

Reason for revert:
Looks like it introduced a top 10 renderer crashing bug, see crbug/506340.

Original issue's description:
> Fix accessibility with out-of-process iframes.
>
> This patch changes the accessibility tree to attach to lookup the RemoteFrame instead of the RenderFrameImpl (which should not exist).
>
> BUG=490831
>
> Committed: https://crrev.com/2e72faf30d6054b942cf1cef942343b209bab371
> Cr-Commit-Position: refs/heads/master@{#336804}

TBR=dmazzoni@chromium.org,nasko@chromium.org,lfg@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=490831
Committed: https://crrev.com/e09a14bf56ddbc27137faa35dfe55c98dad805c0
Cr-Commit-Position: refs/heads/master@{#337129}

[michaeln, 2015-07-01 22:49:59]

Created Revert of Fix accessibility with out-of-process iframes.

[commit-bot: I haz the power, 2015-07-01 22:51:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1221003003/1

[commit-bot: I haz the power, 2015-07-01 22:52:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-01 22:54:00]

Patchset 1 (id:??) landed as
https://crrev.com/e09a14bf56ddbc27137faa35dfe55c98dad805c0
Cr-Commit-Position: refs/heads/master@{#337129}