perf ui/gtk: Add GTK info_bar widget to browser window

The GtkInfoBar is a modern UI component to display messages without
bothering the main window. It'll be used for showing a warning message.

As the GtkInfoBar requires 2.18 (or newer) version of GTK+ library, add
availability check to Makefile too.

Suggested-by: Sunjin Yang <fan4326@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338265382-6872-7-git-send-email-namhyung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/ui/gtk/gtk.h b/tools/perf/ui/gtk/gtk.h
index 2061678..a4d0f2b 100644
--- a/tools/perf/ui/gtk/gtk.h
+++ b/tools/perf/ui/gtk/gtk.h
@@ -10,6 +10,11 @@
 
 struct perf_gtk_context {
 	GtkWidget *main_window;
+
+#ifdef HAVE_GTK_INFO_BAR
+	GtkWidget *info_bar;
+	GtkWidget *message_label;
+#endif
 	GtkWidget *statbar;
 	guint statbar_ctx_id;
 };
@@ -24,4 +29,11 @@
 struct perf_gtk_context *perf_gtk__activate_context(GtkWidget *window);
 int perf_gtk__deactivate_context(struct perf_gtk_context **ctx);
 
+#ifndef HAVE_GTK_INFO_BAR
+static inline GtkWidget *perf_gtk__setup_info_bar(void)
+{
+	return NULL;
+}
+#endif
+
 #endif /* _PERF_GTK_H_ */