Add initial support for key rotation through ce cdm interface.

Merge from Widevine repo of http://go/wvgerrit/42941

Bug: 72168544
Test: tested as part of http://go/ag/4674759
Change-Id: I1a2d0f49371e5b3edf1d9dff85b85593f981d1f5

libwvdrmengine/cdm/core/src/cdm_engine.cpp

@@ -289,7 +289,9 @@ CdmResponseType CdmEngine::GenerateKeyRequest(
   sts = session->GenerateKeyRequest(init_data, license_type, app_parameters,
                                     key_request);
 
-  if (KEY_MESSAGE != sts) {
+  if (KEY_ADDED == sts) {
+    return sts;
+  } else if (KEY_MESSAGE != sts) {
     if (sts == NEED_PROVISIONING) {
       cert_provisioning_requested_security_level_ =
           session->GetRequestedSecurityLevel();