Re-add a (dummy) webrtc/base/buffer.cc to hopefully unbreak the Chromium build

webrtc/base/buffer.cc

Index: webrtc/base/buffer.cc
diff --git a/webrtc/api/mediastreamhandler.cc b/webrtc/base/buffer.cc
similarity index 62%
copy from webrtc/api/mediastreamhandler.cc
copy to webrtc/base/buffer.cc
index 4679037f1ff6673b2773118e2c04d8a220f73df9..79e48bd7a7453bb2c877d9d62b504494fe784ebb 100644
--- a/webrtc/api/mediastreamhandler.cc
+++ b/webrtc/base/buffer.cc
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
+ *  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
@@ -8,5 +8,5 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-// TODO(deadbeef): Remove this file once Chrome build files no longer reference
-// it.
+// This is a dummy file, added because something in the Chromium build claims
+// to need it. We should fix that, and then remove it (bug 5845).