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/modules/video_coding/encoded_frame.cc b/modules/video_coding/encoded_frame.cc
index 3c677f7..aff9c5a 100644
--- a/modules/video_coding/encoded_frame.cc
+++ b/modules/video_coding/encoded_frame.cc
@@ -36,9 +36,9 @@
 
 void VCMEncodedFrame::Free() {
   Reset();
-  if (_buffer != NULL) {
-    delete[] _buffer;
-    _buffer = NULL;
+  if (data() != nullptr) {
+    delete[] data();
+    set_buffer(nullptr, 0);
   }
 }
 
@@ -157,13 +157,13 @@
   size_t old_capacity = capacity();
   if (minimumSize > old_capacity) {
     // create buffer of sufficient size
-    uint8_t* old_buffer = _buffer;
+    uint8_t* old_data = data();
 
     set_buffer(new uint8_t[minimumSize], minimumSize);
-    if (old_buffer) {
+    if (old_data) {
       // copy old data
-      memcpy(_buffer, old_buffer, old_capacity);
-      delete[] old_buffer;
+      memcpy(data(), old_data, old_capacity);
+      delete[] old_data;
     }
   }
 }