MacViews: Disable NativeWidgetMacTest.WindowModalSheet.

ui/views/widget/native_widget_mac_unittest.mm

Index: ui/views/widget/native_widget_mac_unittest.mm
diff --git a/ui/views/widget/native_widget_mac_unittest.mm b/ui/views/widget/native_widget_mac_unittest.mm
index f2e7473693c4f95e1b8475d512bba1365dde43a3..1e0544d2fe7df5989b403b66a699f55c8bfb6079 100644
--- a/ui/views/widget/native_widget_mac_unittest.mm
+++ b/ui/views/widget/native_widget_mac_unittest.mm
@@ -1045,7 +1045,11 @@ TEST_F(NativeWidgetMacTest, NativeWindowChildModalShowHide) {
 }
 
 // Tests behavior of window-modal dialogs, displayed as sheets.
-TEST_F(NativeWidgetMacTest, WindowModalSheet) {
+// Disabled: fails due to sharding adjustments. DCHECK fails during closure when
+// the parent window receives an asynchronous occlusion state change from the
+// window server, after the child has its parent window relationship removed.
+// TODO(tapted): Fix it. http://cbrug.com/666503.
+TEST_F(NativeWidgetMacTest, DISABLED_WindowModalSheet) {
   NSWindow* native_parent =
       MakeNativeParentWithStyle(NSClosableWindowMask | NSTitledWindowMask);