Log timestamps when old frames are delivered.

BUG=webrtc:4994
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1335993003

Cr-Commit-Position: refs/heads/master@{#9928}

webrtc/video/video_capture_input.cc

@@ -101,7 +101,10 @@ void VideoCaptureInput::IncomingCapturedFrame(const VideoFrame& video_frame) {
   CriticalSectionScoped cs(capture_cs_.get());
   if (incoming_frame.ntp_time_ms() <= last_captured_timestamp_) {
     // We don't allow the same capture time for two frames, drop this one.
-    LOG(LS_WARNING) << "Same/old NTP timestamp for incoming frame. Dropping.";
+    LOG(LS_WARNING) << "Same/old NTP timestamp ("
+                    << incoming_frame.ntp_time_ms()
+                    << " <= " << last_captured_timestamp_
+                    << ") for incoming frame. Dropping.";
     return;
   }