Make system modal check more strict

ash/wm/system_modal_container_layout_manager_unittest.cc

Index: ash/wm/system_modal_container_layout_manager_unittest.cc
diff --git a/ash/wm/system_modal_container_layout_manager_unittest.cc b/ash/wm/system_modal_container_layout_manager_unittest.cc
index c8c5b4890ec198e4df37e2fd733b318f891e3168..55f7cc811166a4b9ed200317020ca024864aa666 100644
--- a/ash/wm/system_modal_container_layout_manager_unittest.cc
+++ b/ash/wm/system_modal_container_layout_manager_unittest.cc
@@ -676,6 +676,31 @@ TEST_F(SystemModalContainerLayoutManagerTest, UpdateModalType) {
   EXPECT_FALSE(WmShell::Get()->IsSystemModalWindowOpen());
 }
 
+TEST_F(SystemModalContainerLayoutManagerTest, VisibilityChange) {
+  // Create a modal window.
+  std::unique_ptr<aura::Window> parent(OpenToplevelTestWindow(false));
+  std::unique_ptr<aura::Window> modal_window(
+      OpenTestWindowWithParent(parent.get(), true));
+  parent->Show();
+  modal_window->Show();

[James Cook, 2016/06/27 00:33:43]

optional: Maybe test it prior to modal_window->Show() to exercise
OnWindowAddedToLayout()?

[oshima, 2016/06/27 02:26:07]

Done. (turns out the function was calling show, so I create using view::Widget
API instead)

+  EXPECT_TRUE(WmShell::Get()->IsSystemModalWindowOpen());
+  EXPECT_TRUE(Shell::GetPrimaryRootWindowController()

[James Cook, 2016/06/27 00:33:43]

optional nit: Cache pointer to SystemModalLayoutManager?

[oshima, 2016/06/27 02:26:07]

Done.

+                  ->GetSystemModalLayoutManager(modal_window.get())
+                  ->has_modal_background());
+
+  modal_window->Hide();
+  EXPECT_FALSE(WmShell::Get()->IsSystemModalWindowOpen());
+  EXPECT_FALSE(Shell::GetPrimaryRootWindowController()
+                   ->GetSystemModalLayoutManager(modal_window.get())
+                   ->has_modal_background());
+
+  modal_window->Show();
+  EXPECT_TRUE(WmShell::Get()->IsSystemModalWindowOpen());
+  EXPECT_TRUE(Shell::GetPrimaryRootWindowController()
+                  ->GetSystemModalLayoutManager(modal_window.get())
+                  ->has_modal_background());
+}
+
 namespace {
 
 class InputTestDelegate : public aura::test::TestWindowDelegate {