Fix compositor view caching logic

Fix compositor view caching logic

Previously, each time a SceneLayer was set in the compositor view the
root was checked against the cached root. If the check failed, the
layer would be removed from its parent and the current layer would be
stored.

In the case of scene overlays, the root element can change quite
frequently. In this case, the content of the tree does not necessarily
change, but the root does. This root change would cause the cached
layer to be removed from the new tree before it was rendered.

This change checks that the cached root has the new root as an
ancestor before attempting to detach it.

BUG=584340
Committed: https://crrev.com/734c7ef31f9919be22ba14a258d7ca1c33659d42
Cr-Commit-Position: refs/heads/master@{#381729}

[mdjones, 2016-03-15 21:40:41]

mdjones@chromium.org changed reviewers:
+ dtrainor@chromium.org

[mdjones, 2016-03-15 21:40:41]

PTAL

[David Trainor- moved to gerrit, 2016-03-16 18:36:09]

lgtm

[mdjones, 2016-03-17 15:41:56]

The CQ bit was checked by mdjones@chromium.org

[commit-bot: I haz the power, 2016-03-17 15:42:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1801243003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1801243003/20001

[commit-bot: I haz the power, 2016-03-17 16:27:06]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-03-17 16:28:17]

Description was changed from

==========
Fix compositor view caching logic

Previously, each time a SceneLayer was set in the compositor view the
root was checked against the cached root. If the check failed, the
layer would be removed from its parent and the current layer would be
stored.

In the case of scene overlays, the root element can change quite
frequently. In this case, the content of the tree does not necessarily
change, but the root does. This root change would cause the cached
layer to be removed from the new tree before it was rendered.

This change checks that the cached root has the new root as an
ancestor before attempting to detach it.

BUG=584340
==========

to

==========
Fix compositor view caching logic

Previously, each time a SceneLayer was set in the compositor view the
root was checked against the cached root. If the check failed, the
layer would be removed from its parent and the current layer would be
stored.

In the case of scene overlays, the root element can change quite
frequently. In this case, the content of the tree does not necessarily
change, but the root does. This root change would cause the cached
layer to be removed from the new tree before it was rendered.

This change checks that the cached root has the new root as an
ancestor before attempting to detach it.

BUG=584340

Committed: https://crrev.com/734c7ef31f9919be22ba14a258d7ca1c33659d42
Cr-Commit-Position: refs/heads/master@{#381729}
==========

[commit-bot: I haz the power, 2016-03-17 16:28:18]

Patchset 2 (id:??) landed as
https://crrev.com/734c7ef31f9919be22ba14a258d7ca1c33659d42
Cr-Commit-Position: refs/heads/master@{#381729}