aura: Hide transient children of a Window when the window hides.

ui/aura/window_unittest.cc

Index: ui/aura/window_unittest.cc
diff --git a/ui/aura/window_unittest.cc b/ui/aura/window_unittest.cc
index d989e684558ba15e059c93cbbe6f6f25ee216b73..6795eff38b24e89b4a9cfabaeec7e45f9fda0a87 100644
--- a/ui/aura/window_unittest.cc
+++ b/ui/aura/window_unittest.cc
@@ -1042,6 +1042,11 @@ TEST_F(WindowTest, TransientChildren) {
   ASSERT_EQ(2u, parent->children().size());
   EXPECT_EQ(w3.get(), parent->children()[0]);
   EXPECT_EQ(w1.get(), parent->children()[1]);
+
+  // Hiding parent should hide transient children.
+  EXPECT_TRUE(w2->IsVisible());
+  w1->Hide();
+  EXPECT_FALSE(w2->IsVisible());
 }
 
 // Tests that when a focused window is closed, its parent inherits the focus.