Add setter method EncodedFrame::SetTimestamp.

Similar to the getter method (see
https://webrtc-review.googlesource.com/83123), this is a preparation
for inheriting the method from the base class, and delete the
corresponding redundant timestamp member.

Bug: webrtc:9378
Change-Id: Idbb48e7058c94d6d4aa9a2b19e608ef08c2e35b4
Reviewed-on: https://webrtc-review.googlesource.com/83726
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23665}
diff --git a/api/video/encoded_frame.cc b/api/video/encoded_frame.cc
index ec8877c..f9152b2 100644
--- a/api/video/encoded_frame.cc
+++ b/api/video/encoded_frame.cc
@@ -21,5 +21,9 @@
   return timestamp;
 }
 
+void EncodedFrame::SetTimestamp(uint32_t rtp_timestamp) {
+  timestamp = rtp_timestamp;
+}
+
 }  // namespace video_coding
 }  // namespace webrtc
diff --git a/api/video/encoded_frame.h b/api/video/encoded_frame.h
index 8bfa61e..1b0a26a 100644
--- a/api/video/encoded_frame.h
+++ b/api/video/encoded_frame.h
@@ -58,8 +58,9 @@
 
   virtual bool GetBitstream(uint8_t* destination) const = 0;
 
-  // The capture timestamp of this frame.
+  // The capture timestamp of this frame, using the 90 kHz RTP clock.
   virtual uint32_t Timestamp() const;
+  virtual void SetTimestamp(uint32_t rtp_timestamp);
 
   // When this frame was received.
   virtual int64_t ReceivedTime() const = 0;