Fix nullptr access in CursorRendererAura::SnapshotCursorState.

Fix nullptr access in CursorRendererAura::SnapshotCursorState.

If active_window is nil, we should not call virtual methods on it.

The bug was found by running content_unittests under UBSan.

BUG=607996
Committed: https://crrev.com/25c64861843f487feedf6eaa76acbec96187bb68
Cr-Commit-Position: refs/heads/master@{#428863}

[krasin1, 2016-10-31 21:54:49]

The CQ bit was checked by krasin@chromium.org to run a CQ dry run

[krasin1, 2016-10-31 21:54:59]

krasin@chromium.org changed reviewers:
+ wez@chromium.org

[commit-bot: I haz the power, 2016-10-31 21:55:24]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-31 22:54:14]

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

[commit-bot: I haz the power, 2016-10-31 22:54:14]

Dry run: This issue passed the CQ dry run.

[Wez, 2016-10-31 23:23:26]

The CQ bit was checked by wez@chromium.org

[Wez, 2016-10-31 23:23:27]

lgtm

[commit-bot: I haz the power, 2016-10-31 23:24:14]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-31 23:29:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-31 23:31:28]

Description was changed from

==========
Fix nullptr access in CursorRendererAura::SnapshotCursorState.

If active_window is nil, we should not call virtual methods on it.

The bug was found by running content_unittests under UBSan.

BUG=607996
==========

to

==========
Fix nullptr access in CursorRendererAura::SnapshotCursorState.

If active_window is nil, we should not call virtual methods on it.

The bug was found by running content_unittests under UBSan.

BUG=607996

Committed: https://crrev.com/25c64861843f487feedf6eaa76acbec96187bb68
Cr-Commit-Position: refs/heads/master@{#428863}
==========

[commit-bot: I haz the power, 2016-10-31 23:31:29]

Patchset 1 (id:??) landed as
https://crrev.com/25c64861843f487feedf6eaa76acbec96187bb68
Cr-Commit-Position: refs/heads/master@{#428863}