Always generate nonce before signing license

Merge from Widevine repo of http://go/wvgerrit/135467

The v16 state diagram says that a nonce should be included in all
license requests. The unit tests were not honoring this
requirement. This CL updates the unit tests to match the
spec.

Test: ran unit tests on luci
Bug: 186565384
Change-Id: Ib3e03593538235e2eae3da1732109f0e9bfd97bd

libwvdrmengine/oemcrypto/test/oec_session_util.cpp

@@ -204,6 +204,9 @@ RoundTrip<CoreRequest, PrepAndSignRequest, CoreResponse, ResponseData>::
   size_t gen_signature_length = 0;
   size_t core_message_length = 0;
   constexpr size_t small_size = 42;  // arbitrary.
+  if (RequestHasNonce()) {
+    session()->GenerateNonce();
+  }
   uint32_t session_id = session()->session_id();
   GetDefaultRequestSignatureAndCoreMessageLengths<PrepAndSignRequest>(
       session_id, small_size, &gen_signature_length, &core_message_length);
@@ -294,7 +297,6 @@ OEMCrypto_Substring RoundTrip<CoreRequest, PrepAndSignRequest, CoreResponse,
 void ProvisioningRoundTrip::PrepareSession(
     const wvoec::WidevineKeybox& keybox) {
   ASSERT_NO_FATAL_FAILURE(session_->open());
-  session_->GenerateNonce();
   if (global_features.provisioning_method == OEMCrypto_Keybox) {
     session_->GenerateDerivedKeysFromKeybox(keybox);
     encryptor_ = session_->key_deriver();