Reland of TCRtpReceiver.getContributingSources() added.

third_party/WebKit/public/platform/WebRTCRtpContributingSource.h

+// 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.
+
+#ifndef WebRTCRtpContributingSource_h
+#define WebRTCRtpContributingSource_h
+
+#include "WebCommon.h"
+
+namespace blink {
+
+enum class WebRTCRtpContributingSourceType {
+  SSRC,
+  CSRC,
+};
+
+// https://w3c.github.io/webrtc-pc/#dom-rtcrtpcontributingsource
+class BLINK_PLATFORM_EXPORT WebRTCRtpContributingSource {
+ public:
+  virtual ~WebRTCRtpContributingSource();
+
+  virtual WebRTCRtpContributingSourceType SourceType() const = 0;
+  virtual double TimestampMs() const = 0;
+  virtual uint32_t Source() const = 0;
+};
+
+}  // namespace blink
+
+#endif  // WebRTCRtpContributingSource_h