No need to delete ax subtree when new node is added.

No need to delete ax subtree when new node is added.

AXTreeSerializer was instructing its client to delete the whole
subtree whenever it got a notification on a new node, but that
isn't actually necessary. It was causing the whole tree to be
recreated unneccessarily. Existing unit tests still pass, and
they're comprehensive.

BUG=368295
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=267096

[David Tseng, 2014-04-29 17:30:00]

lgtm

[dmazzoni, 2014-04-29 17:31:00]

The CQ bit was checked by dmazzoni@chromium.org

[commit-bot: I haz the power, 2014-04-29 17:32:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/260463003/1

[commit-bot: I haz the power, 2014-04-29 23:02:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-29 23:02:42]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel on tryserver.chromium

[dmazzoni, 2014-04-30 05:43:41]

The CQ bit was checked by dmazzoni@chromium.org

[commit-bot: I haz the power, 2014-04-30 05:44:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/260463003/1

[commit-bot: I haz the power, 2014-04-30 05:45:34]

Change committed as 267096