Fix a crash that happens when changing themes.

chrome/browser/gtk/nine_box.h

Index: chrome/browser/gtk/nine_box.h
diff --git a/chrome/browser/gtk/nine_box.h b/chrome/browser/gtk/nine_box.h
index dfdfafb196b5fdea62fa4d0c505d60262358738f..4ceea5429fcef29865fe9faed34800f58f51626b 100644
--- a/chrome/browser/gtk/nine_box.h
+++ b/chrome/browser/gtk/nine_box.h
@@ -7,6 +7,10 @@
 
 #include <gtk/gtk.h>
 
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
+#include "chrome/common/notification_type.h"
+
 class ThemeProvider;
 
 // A NineBox manages a set of source images representing a 3x3 grid, where
@@ -20,7 +24,7 @@ class ThemeProvider;
 //
 // TODO(port): add support for caching server-side pixmaps of prerendered
 // nineboxes.
-class NineBox {
+class NineBox : public NotificationObserver {
  public:
   // Construct a NineBox with nine images.  Images are specified using resource
   // ids that will be passed to the resource bundle.  Use 0 for no image.
@@ -52,8 +56,20 @@ class NineBox {
   // needed).
   void ContourWidget(GtkWidget* widget) const;
 
+  // Provide NotificationObserver implementation.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
  private:
   GdkPixbuf* images_[9];
+
+  // We need to remember the image ids that the user passes in and the theme
+  // provider so we can reload images if the user changes theme.
+  int image_ids_[9];
+  ThemeProvider* theme_provider_;
+
+  // Used to listen for theme change notifications.
+  NotificationRegistrar registrar_;
 };
 
 #endif  // CHROME_BROWSER_GTK_NINE_BOX_H_