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

webrtc/BUILD.gn

Index: webrtc/BUILD.gn
diff --git a/webrtc/BUILD.gn b/webrtc/BUILD.gn
index b917566891835d6ab3c51f7eb69787cf8e2f3b92..c08a3c42b6685cc305b67ea69fded0ba81c6ca3a 100644
--- a/webrtc/BUILD.gn
+++ b/webrtc/BUILD.gn
@@ -360,6 +360,13 @@ rtc_static_library("webrtc_common") {
     "typedefs.h",
   ]
 
+  # This is needed here  because common_types.cc uses VideoContentType, which
+  # needs .cc file to be compiled. This is public to allow include of
+  # video_content_type.h.
+  public_deps = [
+    "api:video_content_type_api",
+  ]
+
   if (!build_with_chromium && is_clang) {
     # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]