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

webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
index 3a4afef42558f83e07c2a62a02a0b4150bef6ffc..e3f6474d3657ec8993975e4a60d165d8f81e7744 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
@@ -231,9 +231,8 @@ constexpr const char* VideoContentTypeExtension::kUri;
 
 bool VideoContentTypeExtension::Parse(rtc::ArrayView<const uint8_t> data,
                                       VideoContentType* content_type) {
-  if (data.size() == 1 &&
-      data[0] < static_cast<uint8_t>(VideoContentType::TOTAL_CONTENT_TYPES)) {
-    *content_type = static_cast<VideoContentType>(data[0]);
+  if (data.size() == 1 && VideoContentType::IsValidContentType(data[0])) {

[sprang_webrtc, 2017/07/26 14:13:43]

Maybe be lenient when parsing? Mask out the lowest 6 bit which we know how to
deal with and warn that it contains unknown data.

[ilnik, 2017/07/26 14:49:48]

I think this static one-liner function will be optimized quite well.

+    *content_type = data[0];
     return true;
   }
   return false;