Revert of Re-land: Reimplement automation API on top of C++-backed AXTree.

Revert of Re-land: Reimplement automation API on top of C++-backed AXTree. (patchset #6 id:100001 of https://codereview.chromium.org/1231603009/)

Reason for revert:
Top crasher in today's canary - 74% of browser crashes. Reverting per stability sheriff guidelines (go/stability-sheriff).

Original issue's description:
> Re-land: Reimplement automation API on top of C++-backed AXTree.
>
> Original review: https://codereview.chromium.org/1155183006
> Landed in: r335183
> Reverted in: r335343 (bug 502311)
>
> BUG=495323, 502311
>
> Committed: https://crrev.com/1777fbdbd234ddc8e19d4ba3a42cfd3234b8a158
> Cr-Commit-Position: refs/heads/master@{#339929}

TBR=dcheng@chromium.org,aboxhall@chromium.org,dtseng@chromium.org,kalman@chromium.org,dmazzoni@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=495323, 502311
Committed: https://crrev.com/3cd234a649e3922895a6bb2e4ec786032034bb97
Cr-Commit-Position: refs/heads/master@{#340091}

[Alexei Svitkine (slow), 2015-07-23 14:36:16]

Created Revert of Re-land: Reimplement automation API on top of C++-backed
AXTree.

[commit-bot: I haz the power, 2015-07-23 14:36:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251723003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1251723003/1

[commit-bot: I haz the power, 2015-07-23 14:38:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-23 14:38:44]

Patchset 1 (id:??) landed as
https://crrev.com/3cd234a649e3922895a6bb2e4ec786032034bb97
Cr-Commit-Position: refs/heads/master@{#340091}