Configured VCMTiming with sender defining delay times.

BUG=webrtc:7590

Review-Url: https://codereview.webrtc.org/2870823003
Cr-Commit-Position: refs/heads/master@{#18086}

webrtc/modules/video_coding/frame_buffer2.h

@@ -120,6 +120,11 @@ class FrameBuffer {
 
   using FrameMap = std::map<FrameKey, FrameInfo>;
 
+  // Updates the minimal and maximal playout delays
+  // depending on the frame.
+  void UpdatePlayoutDelays(const FrameObject& frame)
+      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
   // Update all directly dependent and indirectly dependent frames and mark
   // them as continuous if all their references has been fulfilled.
   void PropagateContinuity(FrameMap::iterator start)