Rename EncodedImage::_buffer --> buffer_, and make private

Bug: webrtc:9378
Change-Id: I0a0636077b270a7c73bafafb958132fa648aca70
Reviewed-on: https://webrtc-review.googlesource.com/c/117722
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26294}
diff --git a/api/media_transport_interface.cc b/api/media_transport_interface.cc
index b5eaa89..c1a83bb 100644
--- a/api/media_transport_interface.cc
+++ b/api/media_transport_interface.cc
@@ -95,7 +95,7 @@
   referenced_frame_ids_ = o.referenced_frame_ids_;
   if (!encoded_data_.empty()) {
     // We own the underlying data.
-    encoded_image_._buffer = encoded_data_.data();
+    encoded_image_.set_buffer(encoded_data_.data(), encoded_data_.size());
   }
   return *this;
 }
@@ -110,8 +110,8 @@
   referenced_frame_ids_ = std::move(o.referenced_frame_ids_);
   if (!encoded_data_.empty()) {
     // We take over ownership of the underlying data.
-    encoded_image_._buffer = encoded_data_.data();
-    o.encoded_image_._buffer = nullptr;
+    encoded_image_.set_buffer(encoded_data_.data(), encoded_data_.size());
+    o.encoded_image_.set_buffer(nullptr, 0);
   }
   return *this;
 }