Add CopyOnWriteBuffer class

webrtc/base/BUILD.gn

 # Copyright (c) 2014 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.
 
 import("//build/config/crypto.gni")
 import("//build/config/ui.gni")
@@ skipping 199 matching lines @@
     "asynctcpsocket.cc",
     "asynctcpsocket.h",
     "asyncudpsocket.cc",
     "asyncudpsocket.h",
     "autodetectproxy.cc",
     "autodetectproxy.h",
     "base64.cc",
     "base64.h",
     "common.cc",
     "common.h",
+    "copyonwritebuffer.cc",
+    "copyonwritebuffer.h",
     "crc32.cc",
     "crc32.h",
     "cryptstring.cc",
     "cryptstring.h",
     "diskcache.cc",
     "diskcache.h",
     "filerotatingstream.cc",
     "filerotatingstream.h",
     "fileutils.cc",
     "fileutils.h",
@@ skipping 412 matching lines @@
       "objc/RTCTracing.mm",
     ]
   }
 }
 
 source_set("gtest_prod") {
   sources = [
     "gtest_prod_util.h",
   ]
 }