Add a DecryptCENC call after SelectKey for entitled sessions

Merge from Widevine repo of http://go/wvgerrit/154874

We do not require an error to come from SelectKey immediately, it can
come from a following call to DecryptCENC. This adds a function
Session::TestDecryptCENC to be called instead of SelectKey for the tests
that use entitled sessions.

Bug: 232225906
Test: tested with http://go/ag/20420224

Change-Id: If5695a5034cce371b6eb6bcf1b6467d84456c21d

libwvdrmengine/oemcrypto/test/oec_session_util.h

@@ -561,6 +561,12 @@ class Session {
   void TestDecryptCTR(bool select_key_first = true,
                       OEMCryptoResult expected_result = OEMCrypto_SUCCESS,
                       size_t key_index = 0);
+  // Encrypt some data and pass to OEMCrypto_DecryptCENC to verify decryption
+  // for entitled sessions.
+  void TestDecryptEntitled(OEMCryptoResult expected_result = OEMCrypto_SUCCESS,
+                           OEMCrypto_SESSION session = 0,
+                           const uint8_t* content_key_id = nullptr,
+                           size_t content_key_id_length = 0);
   // Verify that an attempt to select an expired key either succeeds, or gives
   // an actionable error code.
   void TestSelectExpired(size_t key_index);