Added various timestamps to FrameObject.

Added various timestamps to the FrameObject class which are needed to calculate
the jitter delay.

BUG=webrtc:5514

Review-Url: https://codereview.webrtc.org/2124943002
Cr-Commit-Position: refs/heads/master@{#13434}
diff --git a/webrtc/modules/video_coding/packet_buffer.h b/webrtc/modules/video_coding/packet_buffer.h
index ae0916a..ec187de 100644
--- a/webrtc/modules/video_coding/packet_buffer.h
+++ b/webrtc/modules/video_coding/packet_buffer.h
@@ -21,6 +21,9 @@
 #include "webrtc/modules/video_coding/sequence_number_util.h"
 
 namespace webrtc {
+
+class Clock;
+
 namespace video_coding {
 
 class FrameObject;
@@ -35,7 +38,8 @@
 class PacketBuffer {
  public:
   // Both |start_buffer_size| and |max_buffer_size| must be a power of 2.
-  PacketBuffer(size_t start_buffer_size,
+  PacketBuffer(Clock* clock,
+               size_t start_buffer_size,
                size_t max_buffer_size,
                OnCompleteFrameCallback* frame_callback);
 
@@ -68,6 +72,8 @@
     bool frame_created = false;
   };
 
+  Clock* const clock_;
+
   // Tries to expand the buffer.
   bool ExpandBufferSize() EXCLUSIVE_LOCKS_REQUIRED(crit_);