Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Original change: https://codereview.chromium.org/2323103002/

Fix: On Android, the delegate callback called in DestroySubtree was
accessing AXTree::root() after we had deleted it but before we set it
to null. We need to clear it first and then destroy it.

BUG=646777
TBR=aboxhall,mmoroz

Committed: https://crrev.com/5cc41399cda7791ea8edba552304f525b280cfb6
Cr-Commit-Position: refs/heads/master@{#418698}

[dmazzoni, 2016-09-14 20:59:44]

Description was changed from

==========
Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Original change: https://codereview.chromium.org/2323103002/

Fix: On Android, the delegate callback called in DestroySubtree was
accessing AXTree::root() after we had deleted it but before we set it
to null. We need to clear it first and then destroy it.

BUG=646777
==========

to

==========
Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Original change: https://codereview.chromium.org/2323103002/

Fix: On Android, the delegate callback called in DestroySubtree was
accessing AXTree::root() after we had deleted it but before we set it
to null. We need to clear it first and then destroy it.

BUG=646777
TBR=aboxhall,mmoroz
==========

[dmazzoni, 2016-09-14 20:59:44]

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

[dmazzoni, 2016-09-14 20:59:54]

The CQ bit was checked by dmazzoni@chromium.org

[commit-bot: I haz the power, 2016-09-14 21:00:34]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-14 22:33:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-14 22:35:46]

Description was changed from

==========
Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Original change: https://codereview.chromium.org/2323103002/

Fix: On Android, the delegate callback called in DestroySubtree was
accessing AXTree::root() after we had deleted it but before we set it
to null. We need to clear it first and then destroy it.

BUG=646777
TBR=aboxhall,mmoroz
==========

to

==========
Re-land: Add fuzzer for AXTree and fix a couple of bugs it found.

Original change: https://codereview.chromium.org/2323103002/

Fix: On Android, the delegate callback called in DestroySubtree was
accessing AXTree::root() after we had deleted it but before we set it
to null. We need to clear it first and then destroy it.

BUG=646777
TBR=aboxhall,mmoroz

Committed: https://crrev.com/5cc41399cda7791ea8edba552304f525b280cfb6
Cr-Commit-Position: refs/heads/master@{#418698}
==========

[commit-bot: I haz the power, 2016-09-14 22:35:47]

Patchset 1 (id:??) landed as
https://crrev.com/5cc41399cda7791ea8edba552304f525b280cfb6
Cr-Commit-Position: refs/heads/master@{#418698}

[mmoroz, 2016-09-15 14:01:31]

lgtm