New jitter buffer experiment.

BUG=webrtc:5514

Review-Url: https://codereview.webrtc.org/2480293002
Cr-Commit-Position: refs/heads/master@{#15077}
diff --git a/webrtc/modules/video_coding/packet_buffer.h b/webrtc/modules/video_coding/packet_buffer.h
index 15645f6..36b3027 100644
--- a/webrtc/modules/video_coding/packet_buffer.h
+++ b/webrtc/modules/video_coding/packet_buffer.h
@@ -99,8 +99,9 @@
       EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Test if all packets of a frame has arrived, and if so, creates a frame.
-  // May create multiple frames per invocation.
-  void FindFrames(uint16_t seq_num) EXCLUSIVE_LOCKS_REQUIRED(crit_);
+  // Returns a vector of received frames.
+  std::vector<std::unique_ptr<RtpFrameObject>> FindFrames(uint16_t seq_num)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Copy the bitstream for |frame| to |destination|.
   // Virtual for testing.
@@ -108,7 +109,8 @@
 
   // Get the packet with sequence number |seq_num|.
   // Virtual for testing.
-  virtual VCMPacket* GetPacket(uint16_t seq_num);
+  virtual VCMPacket* GetPacket(uint16_t seq_num)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Mark all slots used by |frame| as not used.
   // Virtual for testing.