Reset the window before its acquired layer is deleted

BUG=None
TEST=This should be covered by memory bot. (valgrind/asan should catch this). I'll file a request to add wm_core_unittests to memory bots.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/220813004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261520 0039d316-1c4b-4281-b951-d872f2087c98

ui/wm/core/window_util_unittest.cc

@@ -45,5 +45,8 @@ TEST_F(WindowUtilTest, RecreateLayers) {
   ASSERT_EQ(2u, window1->layer()->children().size());
   EXPECT_EQ(window11->layer(), window1->layer()->children()[0]);
   EXPECT_EQ(window12->layer(), window1->layer()->children()[1]);
+
+  // Delete the window before the acquired layer is deleted.
+  window11.reset();
 }
 }  // namespace wm