Added log messages for important call setup events: first packet sent/received

webrtc/base/onetimeevent.h

Index: webrtc/base/onetimeevent.h
diff --git a/webrtc/base/onetimeevent.h b/webrtc/base/onetimeevent.h
new file mode 100644
index 0000000000000000000000000000000000000000..48cc5752e30979dee06261008d3a359ba883103b
--- /dev/null
+++ b/webrtc/base/onetimeevent.h
@@ -0,0 +1,45 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_ONETIMEEVENT_H_
+#define WEBRTC_BASE_ONETIMEEVENT_H_
+
+#include "webrtc/base/scoped_ptr.h"
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/typedefs.h"
+
+namespace webrtc {
+
+// Provides a simple way to perform an operation (such as logging) one
+// time in a certain scope.
+// Example:
+//   OneTimeEvent firstFrame;
+//   ...
+//   if (firstFrame()) {
+//     LOG(LS_INFO) << "This is the first frame".
+//   }
+class OneTimeEvent {
+ public:
+  OneTimeEvent() {}
+  bool operator()() {
+    rtc::CritScope cs(&critsect_);

[pthatcher1, 2016/03/25 22:35:22]

Would it make sense to allow the OneTimeEvent to choose whether it's thread-safe
or not?  I'm guessing many won't need to be.

And to be extra explicit, we could have a separate class called
ThreadUnsafeOneTimeEvent or something like that.

[skvlad, 2016/03/26 02:00:08]

I've added the thread-unsafe version, however, out of the 5 usages in this CL
(audio/video RTP senders/receivers and VideoReceiver) only one (the
VideoReceiver) is accessing the event while holding a critical section and
therefore can use the thread-unsafe version.

+    bool first_time = !happened_;
+    happened_ = true;
+    return first_time;

[pthatcher1, 2016/03/25 22:35:23]

Might be a little more clear as:

if (happened_) {
  return false;
}
happend_ = true;
return true;

[skvlad, 2016/03/26 02:00:08]

Done.

+  }
+
+ private:
+  bool happened_ = false;
+  rtc::CriticalSection critsect_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_BASE_ONETIMEEVENT_H_