Add CopyOnWriteBuffer class

webrtc/base/copyonwritebuffer.cc

+/*
+ *  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.
+ */
+
+#include "webrtc/base/copyonwritebuffer.h"
+
+namespace rtc {
+
+CopyOnWriteBuffer::CopyOnWriteBuffer() {
+  RTC_DCHECK(IsConsistent());
+}
+
+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(size_t size)
+    : buffer_(size > 0 ? new RefCountedObject<Buffer>(size) : nullptr) {
+  RTC_DCHECK(IsConsistent());
+}
+
+CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size, size_t capacity)
+    : buffer_(size > 0 || capacity > 0
+          ? new RefCountedObject<Buffer>(size, capacity)
+          : nullptr) {
+  RTC_DCHECK(IsConsistent());
+}
+
+CopyOnWriteBuffer::~CopyOnWriteBuffer() = default;
+
+}  // namespace rtc