Add always-on-top property to app windows

ui/views/widget/widget.h

Index: ui/views/widget/widget.h
diff --git a/ui/views/widget/widget.h b/ui/views/widget/widget.h
index 151d2f3028d0100b7946586ad398d04868bf9841..77b4ae680b436ad37e0b813ab8ad4d73b92f031a 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -461,6 +461,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // Sets the widget to be on top of all other widgets in the windowing system.
   void SetAlwaysOnTop(bool on_top);
 
+  // Returns whether the widget has been set to be on top of most other widgets
+  // in the windowing system.
+  bool IsAlwaysOnTop() const;
+
   // Maximizes/minimizes/restores the window.
   void Maximize();
   void Minimize();
@@ -889,6 +893,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // disabled.
   bool movement_disabled_;
 
+  // Cached value of isAlwaysOnTop(). If true, the widget stays on top of
+  // widgets that do not have this flag enabled.
+  bool is_always_on_top_;
+
   DISALLOW_COPY_AND_ASSIGN(Widget);
 };