Add always-on-top property to app windows

ui/views/widget/native_widget_aura.cc

Index: ui/views/widget/native_widget_aura.cc
diff --git a/ui/views/widget/native_widget_aura.cc b/ui/views/widget/native_widget_aura.cc
index 2c22fbece18fe662289a196507a61d4f54e7f7c1..f22bbcee060208171ad4e195c07fb0831568dcf3 100644
--- a/ui/views/widget/native_widget_aura.cc
+++ b/ui/views/widget/native_widget_aura.cc
@@ -534,6 +534,10 @@ void NativeWidgetAura::SetAlwaysOnTop(bool on_top) {
     window_->SetProperty(aura::client::kAlwaysOnTopKey, on_top);
 }
 
+bool NativeWidgetAura::IsAlwaysOnTop() const {
+  return window_ && window_->GetProperty(aura::client::kAlwaysOnTopKey);
+}
+
 void NativeWidgetAura::Maximize() {
   if (window_)
     window_->SetProperty(aura::client::kShowStateKey, ui::SHOW_STATE_MAXIMIZED);