Fix same crashy assumption that I fixed in r20967 later on in normal theme mode.

chrome/browser/gtk/gtk_chrome_button.cc

Index: chrome/browser/gtk/gtk_chrome_button.cc
diff --git a/chrome/browser/gtk/gtk_chrome_button.cc b/chrome/browser/gtk/gtk_chrome_button.cc
index 370ded1d7e46d89efc4d543916422c405b9a59e2..0fc34804ab649e78e49306afb7d27a073e349f6f 100644
--- a/chrome/browser/gtk/gtk_chrome_button.cc
+++ b/chrome/browser/gtk/gtk_chrome_button.cc
@@ -117,9 +117,12 @@ static gboolean gtk_chrome_button_expose(GtkWidget* widget,
     if (nine_box)
       nine_box->RenderToWidget(widget);
 
-    gtk_container_propagate_expose(GTK_CONTAINER(widget),
-                                   gtk_bin_get_child(GTK_BIN(widget)),
-                                   event);
+    // If we have a child widget, draw it.
+    if (gtk_bin_get_child(GTK_BIN(widget))) {
+      gtk_container_propagate_expose(GTK_CONTAINER(widget),
+                                     gtk_bin_get_child(GTK_BIN(widget)),
+                                     event);
+    }
   }
 
   return TRUE;  // Don't propagate, we are the default handler.