Force property_trees rebuild for DamageTrackerTest

Force property_trees rebuild for DamageTrackerTest

DamageTrackerTest does a lot of impl side operations that could not
happen in practice, e.g. LayerImpl::SetPosition(),
LayerImpl::Add/RemoveChild(). These operations won't trigger property
trees rebuild/update so the verification on draw_transform would fail.

The simple fix in this case seems to be forcing a property trees
rebuild.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/5032027d92f1def6b0cc8a35607ad7bc74a56944
Cr-Commit-Position: refs/heads/master@{#333638}

[Yufeng Shen (Slow to review), 2015-06-10 00:06:14]

miletus@chromium.org changed reviewers:
+ enne@chromium.org

[enne (OOO), 2015-06-10 00:09:54]

lgtm

(Also, no need for a BUG=none line.  You can remove that.)

[Yufeng Shen (Slow to review), 2015-06-10 00:16:06]

The CQ bit was checked by miletus@chromium.org

[commit-bot: I haz the power, 2015-06-10 00:17:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1170383003/1

[commit-bot: I haz the power, 2015-06-10 01:27:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-10 01:28:43]

Patchset 1 (id:??) landed as
https://crrev.com/5032027d92f1def6b0cc8a35607ad7bc74a56944
Cr-Commit-Position: refs/heads/master@{#333638}