Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/api/video/video_content_type.cc

+/*
+ *  Copyright (c) 2017 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/api/video/video_content_type.h"
+#include "webrtc/rtc_base/checks.h"
+
+namespace webrtc {
+const VideoContentType VideoContentType::UNSPECIFIED = VideoContentType({0});
+const VideoContentType VideoContentType::SCREENSHARE = VideoContentType({1});
+
+VideoContentType::operator uint8_t() const {
+  return content_type;
+}
+
+uint8_t VideoContentType::operator=(uint8_t value) {
+  content_type = value;
+  return value;
+}
+
+bool VideoContentType::operator==(const VideoContentType& other) {
+  return content_type == other.content_type;
+}

[sprang_webrtc, 2017/08/24 09:13:16]

\n

[ilnik, 2017/08/25 12:35:07]

Done.

+bool VideoContentType::operator==(uint8_t value) {
+  return content_type == value;
+}
+
+void VideoContentType::SetExperimentId(uint8_t experiment_id) {
+  // Store in bits 3-5.
+  RTC_DCHECK(experiment_id < (1 << 3));
+  content_type = (content_type & 0b11000111) | ((experiment_id & 0b111) << 3);

[sprang_webrtc, 2017/08/24 09:13:16]

Could you document the format in a comment at the top of this file?
I'm thinking along the lines of how it's done for RTP wire format parsing.
Then define some static mask constants.

[ilnik, 2017/08/25 12:35:07]

Done.

+}
+
+void VideoContentType::SetSimulcastId(uint8_t simulcast_id) {
+  // Store in bits 1-2.
+  RTC_DCHECK(simulcast_id < (1 << 2));
+  content_type = (content_type & 0b11111001) | ((simulcast_id & 0b11) << 1);
+}
+
+uint8_t VideoContentType::GetExperimentId() const {
+  return (content_type >> 3) & 0b111;
+}
+
+uint8_t VideoContentType::GetSimulcastId() const {
+  return (content_type >> 1) & 0b11;
+}
+
+bool VideoContentType::IsValidContentType(uint8_t value) {
+  // Any 6-bit value is allowed.
+  return value < (1 << 6);
+}
+
+bool VideoContentType::IsScreenshare() const {
+  return (content_type & 1) > 0;
+}
+
+}  // namespace webrtc