Reset the system background before root window is released.

The system background is observing the root and has to deregister itself before the root's release.

BUG=None
TEST=valgrind doesn't report the memory error in ash_unittests for this.

Review URL: https://codereview.chromium.org/11345018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@164783 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed