Support for group license

Content keys in ECM v3 can now additionally be encrypted by group
entitlement keys.

example/wv_cas_ecm_example.cc

@@ -12,6 +12,7 @@
 #include <stdio.h>
 
 #include <cassert>
+#include <cstdint>
 #include <fstream>
 #include <iostream>
 #include <string>
@@ -166,11 +167,12 @@ int main(int argc, char** argv) {
   std::string ecm;
   widevine::Status status;
   if (kKeyRotation) {
-    status = wv_cas_ecm.GenerateEcm(content_keys[0], content_keys[1],
-                                    kDefaultTrackTypeSd, &ecm);
+    status =
+        wv_cas_ecm.GenerateEcm(content_keys[0], content_keys[1],
+                               kDefaultTrackTypeSd, /*group_ids=*/{}, &ecm);
   } else {
-    status = wv_cas_ecm.GenerateSingleKeyEcm(content_keys[0],
-                                             kDefaultTrackTypeSd, &ecm);
+    status = wv_cas_ecm.GenerateSingleKeyEcm(
+        content_keys[0], kDefaultTrackTypeSd, /*group_ids=*/{}, &ecm);
   }
 
   if (!status.ok()) {