Separate key session SelectKey methods

Test: CE CDM tests, Android unit/integration tests
Bug: b/124773017
Merge of http://go/wvgerrit/73144

Since OEMCrypto supports one content key per entitlement key,
LoadEntitledContentKeys must be called every time we want to select a
key. EntitlementKeySession::SelectKey calls ContentKeySession::SelectKey
after loading the keys, which caches the key id from the previous call,
and if the key id hasn't changed, doesn't call SelectKey. This caching
is fine for content keys since we don't call LoadKeys every time, but
not fine for entitled keys since we do call LoadEntitledContentKeys
every time. So, we instead cache the current content key id per
entitlement key and only call LoadEntitledContentKeys and SelectKey if
the entitled content key id changes. Furthermore, the test
HandlesKeyRotationWithOnlyOneLicenseRequest is modified to complete
multiple decrypts per key to test this behavior.

Change-Id: I9d0d94e49da0fe1965beadbddec99d8dff744d73

libwvdrmengine/cdm/core/include/entitlement_key_session.h

@@ -44,7 +44,10 @@ class EntitlementKeySession : public ContentKeySession {
   OEMCrypto_EntitledContentKeyObject MakeOecEntitledKey(
       const CryptoKey& input_key, std::string& message);
 
-  std::map<std::string, CryptoKey> entitled_keys_;
+  // Find the CryptoKey for the given entitled content key id.
+  std::map<KeyId, CryptoKey> entitled_keys_;
+  // Find the current entitled content key id for the given entitlement key id.
+  std::map<KeyId, KeyId> current_loaded_content_keys_;
 };
 
 }  // namespace wvcdm