Added log messages for some important call setup events:

- First audio RTP packet sent / received
 - First RTP packet of the first video frame sent / received
 - Last RTP packet of the first video frame sent / received
These timestamps should make it easier to measure how fast the call
becomes established from the user's perspective.

Review URL: https://codereview.webrtc.org/1765443002

Cr-Commit-Position: refs/heads/master@{#12287}

webrtc/modules/video_coding/jitter_buffer.cc

@@ -1282,9 +1282,13 @@ void VCMJitterBuffer::CountFrame(const VCMFrameBuffer& frame) {
   if (frame.IsSessionComplete()) {
     if (frame.FrameType() == kVideoFrameKey) {
       ++receive_statistics_.key_frames;
+      if (receive_statistics_.key_frames == 1) {
+        LOG(LS_INFO) << "Received first complete key frame";
+      }
     } else {
       ++receive_statistics_.delta_frames;
     }
+
     if (stats_callback_ != NULL)
       stats_callback_->OnFrameCountsUpdated(receive_statistics_);
   }

webrtc/modules/video_coding/video_coding_impl.h

@@ -16,6 +16,7 @@
 #include <memory>
 #include <vector>
 
+#include "webrtc/base/onetimeevent.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/base/thread_checker.h"
 #include "webrtc/modules/video_coding/codec_database.h"
@@ -219,6 +220,7 @@ class VideoReceiver {
   VCMProcessTimer _retransmissionTimer;
   VCMProcessTimer _keyRequestTimer;
   QpParser qp_parser_;
+  ThreadUnsafeOneTimeEvent first_frame_received_;
 };
 
 }  // namespace vcm

webrtc/modules/video_coding/video_receiver.cc

@@ -323,6 +323,13 @@ int32_t VideoReceiver::Decode(uint16_t maxWaitTimeMs) {
     }
   }
 #endif
+
+  if (first_frame_received_()) {
+    LOG(LS_INFO) << "Received first "
+                 << (frame->Complete() ? "complete" : "incomplete")
+                 << " decodable video frame";
+  }
+
   const int32_t ret = Decode(*frame);
   _receiver.ReleaseFrame(frame);
   return ret;