Remove unused instance tree related member variable

Remove unused instance tree related member variable

The plan is to remove the instance tree. Independent of that, this
member variable seems to be set but not used.

BUG=313438
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172707

[rwlbuis, 2014-04-27 02:30:37]

Simple cleanup, as a first small step to removing instance tree.

[pdr., 2014-04-27 02:33:47]

On 2014/04/27 02:30:37, rwlbuis wrote:
> Simple cleanup, as a first small step to removing instance tree.

LGTM

[pdr., 2014-04-27 02:35:28]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2014-04-27 02:35:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rob.buis@samsung.com/254803008/1

[commit-bot: I haz the power, 2014-04-27 03:56:01]

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

[commit-bot: I haz the power, 2014-04-27 03:56:01]

Try jobs failed on following builders:
  tryserver.blink on linux_blink_dbg

[pdr., 2014-04-27 04:05:59]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2014-04-27 04:06:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rob.buis@samsung.com/254803008/1

[commit-bot: I haz the power, 2014-04-27 05:25:09]

Change committed as 172707