GTK: Buttons on Confirm Infobars should have matching sizes.

chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h

Index: chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h
diff --git a/chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h b/chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h
index dce45da0db56982bc0bd3f814e0d624b62167bd4..8fc0ac72603104eb2faf0c8c2d01a9d8d3593d4f 100644
--- a/chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h
+++ b/chrome/browser/ui/gtk/infobars/confirm_infobar_gtk.h
@@ -11,6 +11,7 @@
 #include "chrome/browser/ui/gtk/infobars/infobar_gtk.h"
 #include "ui/base/gtk/gtk_signal.h"
 
+typedef struct _GtkSizeGroup GtkSizeGroup;
 typedef struct _GtkWidget GtkWidget;
 
 // An infobar that shows a message, up to two optional buttons, and an optional,
@@ -33,6 +34,8 @@ class ConfirmInfoBarGtk : public InfoBar {
 
   GtkWidget* confirm_hbox_;
 
+  GtkSizeGroup* size_group_;
+
   DISALLOW_COPY_AND_ASSIGN(ConfirmInfoBarGtk);
 };