RTCRtpReceiver.getContributingSources() added.

third_party/WebKit/Source/platform/exported/WebRTCRtpContributingSource.cpp

Index: third_party/WebKit/Source/platform/exported/WebRTCRtpContributingSource.cpp
diff --git a/third_party/WebKit/Source/platform/exported/WebRTCRtpContributingSource.cpp b/third_party/WebKit/Source/platform/exported/WebRTCRtpContributingSource.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e8480b04b57869053d3e8e33a3469353f5c60481
--- /dev/null
+++ b/third_party/WebKit/Source/platform/exported/WebRTCRtpContributingSource.cpp
@@ -0,0 +1,11 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "public/platform/WebRTCRtpContributingSource.h"
+
+namespace blink {
+
+WebRTCRtpContributingSource::~WebRTCRtpContributingSource() {}
+
+}  // namespace blink