Generate Key Set IDs at Key Request Generation Time

(This is a merge of http://go/wvgerrit/11285 from the Widevine CDM
repository.)

The key set ID is now available earlier, in order to support the CE
CDM 4.5 interface, which needs it at key request generation time, not
later at key response receipt time. It is still possible to receive
the key set ID at key response time, for Android's purposes. Either
API may now be passed a pointer to store the ID in, which may also be
left NULL if this is not needed.

Change-Id: I47e80ea4005c80282e36cfae92cb91142208f624

libwvdrmengine/cdm/core/include/cdm_session.h

@@ -36,7 +36,7 @@ class CdmSession {
   virtual CdmResponseType GenerateKeyRequest(
       const InitializationData& init_data, const CdmLicenseType license_type,
       const CdmAppParameterMap& app_parameters, CdmKeyMessage* key_request,
-      std::string* server_url);
+      std::string* server_url, CdmKeySetId* key_set_id);
 
   // AddKey() - Accept license response and extract key info.
   virtual CdmResponseType AddKey(const CdmKeyResponse& key_response,