Allow using system libevent instead of the bundled one.

base/message_pump_libevent.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/message_pump_libevent.h"
 
 #include <errno.h>
 #include <fcntl.h>
 
 #include "eintr_wrapper.h"
 #include "base/auto_reset.h"
 #include "base/logging.h"
 #include "base/scoped_nsautorelease_pool.h"
 #include "base/scoped_ptr.h"
 #include "base/time.h"
+#if defined(USE_SYSTEM_LIBEVENT)
+#include <event.h>
+#else
 #include "third_party/libevent/event.h"
+#endif
 
 // Lifecycle of struct event
 // Libevent uses two main data structures:
 // struct event_base (of which there is one per message pump), and
 // struct event (of which there is roughly one per socket).
 // The socket's struct event is created in
 // MessagePumpLibevent::WatchFileDescriptor(),
 // is owned by the FileDescriptorWatcher, and is destroyed in
 // StopWatchingFileDescriptor().
 // It is moved into and out of lists in struct event_base by
@@ skipping 267 matching lines @@
 }
 
 void MessagePumpLibevent::ScheduleDelayedWork(const Time& delayed_work_time) {
   // We know that we can't be blocked on Wait right now since this method can
   // only be called on the same thread as Run, so we only need to update our
   // record of how long to sleep when we do sleep.
   delayed_work_time_ = delayed_work_time;
 }
 
 }  // namespace base