Implement CopyOnWriteBuffer move using scoped_refptr move

webrtc/base/copyonwritebuffer.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 101 matching lines @@
     RTC_DCHECK(buf.IsConsistent());
     if (&buf != this) {
       buffer_ = buf.buffer_;
     }
     return *this;
   }
 
   CopyOnWriteBuffer& operator=(CopyOnWriteBuffer&& buf) {
     RTC_DCHECK(IsConsistent());
     RTC_DCHECK(buf.IsConsistent());
-    // TODO(jbauch): use std::move once scoped_refptr supports it (issue 5556)
-    buffer_.swap(buf.buffer_);
-    buf.buffer_ = nullptr;
+    buffer_ = std::move(buf.buffer_);
     return *this;
   }
 
   bool operator==(const CopyOnWriteBuffer& buf) const {
     // Must either use the same buffer internally or have the same contents.
     RTC_DCHECK(IsConsistent());
     RTC_DCHECK(buf.IsConsistent());
     return buffer_.get() == buf.buffer_.get() ||
         (buffer_.get() && buf.buffer_.get() &&
         *buffer_.get() == *buf.buffer_.get());
@@ skipping 148 matching lines @@
     return (!buffer_ || buffer_->capacity() > 0);
   }
 
   // buffer_ is either null, or points to an rtc::Buffer with capacity > 0.
   scoped_refptr<RefCountedObject<Buffer>> buffer_;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_COPYONWRITEBUFFER_H_