Add always-on-top property to app windows

chrome/browser/ui/gtk/apps/native_app_window_gtk.h

Index: chrome/browser/ui/gtk/apps/native_app_window_gtk.h
diff --git a/chrome/browser/ui/gtk/apps/native_app_window_gtk.h b/chrome/browser/ui/gtk/apps/native_app_window_gtk.h
index 6cb9c9b61c5972d26825cbce5614907e23ec402a..302da4ece8f54f18b1e79e3525878efa14f9bfa9 100644
--- a/chrome/browser/ui/gtk/apps/native_app_window_gtk.h
+++ b/chrome/browser/ui/gtk/apps/native_app_window_gtk.h
@@ -80,6 +80,7 @@ class NativeAppWindowGtk : public apps::NativeAppWindow,
   virtual bool IsVisible() const OVERRIDE;
   virtual void HideWithApp() OVERRIDE;
   virtual void ShowWithApp() OVERRIDE;
+  virtual void SetAlwaysOnTop(bool always_on_top) OVERRIDE;
 
   // web_modal::WebContentsModalDialogHost implementation.
   virtual gfx::NativeView GetHostView() const OVERRIDE;
@@ -154,6 +155,10 @@ class NativeAppWindowGtk : public apps::NativeAppWindow,
   // True if the window should be resizable by the user.
   bool resizable_;
 
+  // True if the window should be kept on top of other windows that do not have
+  // this flag enabled.
+  bool always_on_top_;
+
   // The current window cursor.  We set it to a resize cursor when over the
   // custom frame border.  We set it to NULL if we want the default cursor.
   GdkCursor* frame_cursor_;