Add a mechanism to extend a libevent based message pump.

message_loop/message_loop.cc

Index: message_loop/message_loop.cc
diff --git a/message_loop/message_loop.cc b/message_loop/message_loop.cc
index 6bd6730cde34752a3e7db50ee8d2f153379013da..bd8e47673f1f8cc5a9934de6be3a386d74ef0831 100644
--- a/message_loop/message_loop.cc
+++ b/message_loop/message_loop.cc
@@ -708,6 +708,17 @@ bool MessageLoopForUI::WatchFileDescriptor(
 }
 #endif
 
+#if defined(USE_X11)
+void MessageLoopForUI::SetEventSource(
+    MessagePumpLibevent::EventSource* event_source) {
+  static_cast<MessagePumpLibevent*>(pump_.get())->SetEventSource(event_source);
+}
+
+void MessageLoopForUI::ClearEventSource() {
+  static_cast<MessagePumpLibevent*>(pump_.get())->ClearEventSource();
+}
+#endif
+
 #endif  // !defined(OS_NACL)
 
 //------------------------------------------------------------------------------