Revert of Refactor content/renderer/accessibility to use AXTreeSerializer.

Revert of Refactor content/renderer/accessibility to use AXTreeSerializer. (https://codereview.chromium.org/125763003/)

Reason for revert:
Breaks asan builders: http://build.chromium.org/p/chromium.memory/buildstatus?builder=Linux%20ASan%2BLSan%20Tests%20%283%29&number=1347

Original issue's description:
> Refactor content/renderer/accessibility to use AXTreeSerializer.
> 
> This removes the confusing code in content/renderer/accessibility that
> serializes updates from Blink's accessibility tree, and replaces it with
> calls to the new cleaner and fully-unit-tested AXTreeSerializer class.
> 
> BUG=316726
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=261099

TBR=dtseng@chromium.org,aboxhall@chromium.org,tsepez@chromium.org,jam@chromium.org,aarya@google.com,dmazzoni@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=316726
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=261107

[pfeldman, 2014-04-02 11:29:45]

Created Revert of Refactor content/renderer/accessibility to use
AXTreeSerializer.

[commit-bot: I haz the power, 2014-04-02 11:29:50]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pfeldman@chromium.org/222073002/1

[commit-bot: I haz the power, 2014-04-02 11:31:36]

Change committed as 261107