Remove remaining window states where window is shown with opacity 0.

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 2c9aab82d83b371a3d53047c2822992457062638..899fdfdb047c14b76f8a72ce270380c75eb911c7 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -339,8 +339,7 @@ void Window::Show() {
     // It is not allowed that a window is visible but the layers alpha is fully
     // transparent since the window would still be considered to be active but
     // could not be seen.
-    // TODO(skuhne): uncomment and fix issue 351553.
-    // DCHECK(!(visible_ && layer()->GetTargetOpacity() == 0.0f));
+    DCHECK(!(visible_ && layer()->GetTargetOpacity() == 0.0f));
   }
   SetVisible(true);
 }