Reland of Add content type information to encoded images and corresponding rtp extension header

webrtc/test/constants.cc

Index: webrtc/test/constants.cc
diff --git a/webrtc/test/constants.cc b/webrtc/test/constants.cc
index 43f9adc3340d152fab49c5c18671374d226adfb2..a789cc0df66474e0548ea250044b0536cedc6416 100644
--- a/webrtc/test/constants.cc
+++ b/webrtc/test/constants.cc
@@ -17,5 +17,7 @@ const int kTOffsetExtensionId = 6;
 const int kAbsSendTimeExtensionId = 7;
 const int kTransportSequenceNumberExtensionId = 8;
 const int kVideoRotationExtensionId = 9;
+const int kVideoContentTypeExtensionId = 10;
+
 }  // namespace test
 }  // namespace webrtc