Change VCMFrameBuffer and VCMEncodedFrame to use rotation from base class EncodedImage.

BUG=webrtc:5687

Review-Url: https://codereview.webrtc.org/2037633002
Cr-Commit-Position: refs/heads/master@{#13376}
diff --git a/webrtc/modules/video_coding/frame_buffer.cc b/webrtc/modules/video_coding/frame_buffer.cc
index 61db0d1..1c7301f 100644
--- a/webrtc/modules/video_coding/frame_buffer.cc
+++ b/webrtc/modules/video_coding/frame_buffer.cc
@@ -153,7 +153,7 @@
   // (HEVC)).
   if (packet.markerBit) {
     RTC_DCHECK(!_rotation_set);
-    _rotation = packet.video_header.rotation;
+    rotation_ = packet.video_header.rotation;
     _rotation_set = true;
   }