Implement CopyOnWriteBuffer move using scoped_refptr move

webrtc/base/copyonwritebuffer.cc

Index: webrtc/base/copyonwritebuffer.cc
diff --git a/webrtc/base/copyonwritebuffer.cc b/webrtc/base/copyonwritebuffer.cc
index 293faec001b1bfb577a37ef226e3c4c34df8d184..6eae42626bff9d55ab6e5398ffde3434619579ab 100644
--- a/webrtc/base/copyonwritebuffer.cc
+++ b/webrtc/base/copyonwritebuffer.cc
@@ -20,9 +20,8 @@ CopyOnWriteBuffer::CopyOnWriteBuffer(const CopyOnWriteBuffer& buf)
     : buffer_(buf.buffer_) {
 }
 
-CopyOnWriteBuffer::CopyOnWriteBuffer(CopyOnWriteBuffer&& buf) {
-  // TODO(jbauch): use std::move once scoped_refptr supports it (issue 5556)
-  std::swap(buffer_, buf.buffer_);
+CopyOnWriteBuffer::CopyOnWriteBuffer(CopyOnWriteBuffer&& buf)
+    : buffer_(std::move(buf.buffer_)) {
 }
 
 CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size)