Add a mechanism to extend a libevent based message pump.

message_loop/message_pump_libevent.cc

Index: message_loop/message_pump_libevent.cc
diff --git a/message_loop/message_pump_libevent.cc b/message_loop/message_pump_libevent.cc
index 74602a7b3204357e84ac1c8c40abaa4325f37398..b24a10974cd716738484353a0fbaafb56d2376a4 100644
--- a/message_loop/message_pump_libevent.cc
+++ b/message_loop/message_pump_libevent.cc
@@ -119,7 +119,8 @@ MessagePumpLibevent::MessagePumpLibevent()
       processed_io_events_(false),
       event_base_(event_base_new()),
       wakeup_pipe_in_(-1),
-      wakeup_pipe_out_(-1) {
+      wakeup_pipe_out_(-1),
+      event_source_(nullptr) {
   if (!Init())
      NOTREACHED();
 }
@@ -214,6 +215,16 @@ void MessagePumpLibevent::RemoveIOObserver(IOObserver *obs) {
   io_observers_.RemoveObserver(obs);
 }
 
+void MessagePumpLibevent::SetEventSource(EventSource* event_source) {
+  DCHECK(event_source);
+  DCHECK(!event_source_ || event_source_ == event_source);
+  event_source_ = event_source;
+}
+
+void MessagePumpLibevent::ClearEventSource() {
+  event_source_ = nullptr;
+}
+
 // Tell libevent to break out of inner loop.
 static void timer_callback(int fd, short events, void *context)
 {
@@ -238,6 +249,10 @@ void MessagePumpLibevent::Run(Delegate* delegate) {
     if (!keep_running_)
       break;
 
+    did_work |= PollEventSource();
+    if (!keep_running_)
+      break;
+
     event_base_loop(event_base_, EVLOOP_NONBLOCK);
     did_work |= processed_io_events_;
     processed_io_events_ = false;
@@ -316,6 +331,10 @@ void MessagePumpLibevent::DidProcessIOEvent() {
   FOR_EACH_OBSERVER(IOObserver, io_observers_, DidProcessIOEvent());
 }
 
+bool MessagePumpLibevent::PollEventSource() {
+  return event_source_ && event_source_->Poll();
+}
+
 bool MessagePumpLibevent::Init() {
   int fds[2];
   if (pipe(fds)) {