Add accessor methods for RTP timestamp of EncodedImage.

Intention is to make the member private, but downstream callers
must be updated to use the accessor methods first.

Bug: webrtc:9378
Change-Id: I3495bd8d545b7234fbea10abfd14f082caa420b6
Reviewed-on: https://webrtc-review.googlesource.com/82160
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24352}
diff --git a/modules/video_coding/frame_buffer2_unittest.cc b/modules/video_coding/frame_buffer2_unittest.cc
index 1378be5..357ba86 100644
--- a/modules/video_coding/frame_buffer2_unittest.cc
+++ b/modules/video_coding/frame_buffer2_unittest.cc
@@ -90,8 +90,6 @@
  public:
   bool GetBitstream(uint8_t* destination) const override { return true; }
 
-  uint32_t Timestamp() const override { return timestamp; }
-
   int64_t ReceivedTime() const override { return 0; }
 
   int64_t RenderTime() const override { return _renderTimeMs; }
@@ -165,7 +163,7 @@
     std::unique_ptr<FrameObjectFake> frame(new FrameObjectFake());
     frame->id.picture_id = picture_id;
     frame->id.spatial_layer = spatial_layer;
-    frame->timestamp = ts_ms * 90;
+    frame->SetTimestamp(ts_ms * 90);
     frame->num_references = references.size();
     frame->inter_layer_predicted = inter_layer_predicted;
     for (size_t r = 0; r < references.size(); ++r)
@@ -520,7 +518,7 @@
     frame->SetSize(kFrameSize);
     frame->id.picture_id = pid;
     frame->id.spatial_layer = 0;
-    frame->timestamp = ts;
+    frame->SetTimestamp(ts);
     frame->num_references = 0;
     frame->inter_layer_predicted = false;