Revert "Delete the non-const version of the EncodedImage::data() method."

This reverts commit f2969fa868f4913583e79f74ceced5cc6b7d6b7d.

Reason for revert: Breaks blink_platform_unittests; sample failure:
https://ci.chromium.org/p/chromium/builders/try/linux-rel/500046

Original change's description:
> Delete the non-const version of the EncodedImage::data() method.
>
> Bug: webrtc:9378
> Change-Id: I84ace3ca6a2eb4d0f7c3d4e62f815d77df581bfa
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185122
> Reviewed-by: Artem Titov <titovartem@webrtc.org>
> Reviewed-by: Philip Eliasson <philipel@webrtc.org>
> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#32197}

TBR=ilnik@webrtc.org,nisse@webrtc.org,philipel@webrtc.org,titovartem@webrtc.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: webrtc:9378
Change-Id: I6374d263e2ee10da318ab1e040ed18bed7a96edd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185507
Reviewed-by: Marina Ciocea <marinaciocea@webrtc.org>
Commit-Queue: Marina Ciocea <marinaciocea@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32205}
diff --git a/modules/video_coding/frame_object.cc b/modules/video_coding/frame_object.cc
index d58aa10..bdb43f7 100644
--- a/modules/video_coding/frame_object.cc
+++ b/modules/video_coding/frame_object.cc
@@ -38,8 +38,7 @@
     const absl::optional<webrtc::ColorSpace>& color_space,
     RtpPacketInfos packet_infos,
     rtc::scoped_refptr<EncodedImageBuffer> image_buffer)
-    : image_buffer_(image_buffer),
-      first_seq_num_(first_seq_num),
+    : first_seq_num_(first_seq_num),
       last_seq_num_(last_seq_num),
       last_packet_received_time_(last_packet_received_time),
       times_nacked_(times_nacked) {
@@ -61,7 +60,7 @@
   // as of the first packet's.
   SetPlayoutDelay(rtp_video_header_.playout_delay);
 
-  SetEncodedData(image_buffer_);
+  SetEncodedData(std::move(image_buffer));
   _encodedWidth = rtp_video_header_.width;
   _encodedHeight = rtp_video_header_.height;