MacViews: Trigger shadow invalidation when a translucent window is shown.

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 5ae9c03a58f71ea4f5fb5b9df7ca4dd630e02198..0dec9ded50095c597488f9b4f621fe55f2e16cf5 100644
--- a/ui/views/widget/native_widget_mac_unittest.mm
+++ b/ui/views/widget/native_widget_mac_unittest.mm
@@ -1376,6 +1376,17 @@ new ModalDialogDelegate(ui::MODAL_TYPE_CHILD), nullptr,
   test_api.SimulateFrameSwap(gfx::Size(123, 456));
   EXPECT_EQ(2, [window invalidateShadowCount]);
 
+  // Hiding the window does not require shadow invalidation.
+  widget->Hide();
+  test_api.SimulateFrameSwap(gfx::Size(123, 456));
+  EXPECT_EQ(2, [window invalidateShadowCount]);
+
+  // Showing a translucent window after hiding it, should trigger shadow
+  // invalidation.
+  widget->Show();
+  test_api.SimulateFrameSwap(gfx::Size(123, 456));
+  EXPECT_EQ(3, [window invalidateShadowCount]);
+
   widget->CloseNow();
 }