Properly determine if a new key was added in AesDecryptor::Update()

media/cdm/aes_decryptor.h

Index: media/cdm/aes_decryptor.h
diff --git a/media/cdm/aes_decryptor.h b/media/cdm/aes_decryptor.h
index 99b83db9a7d737b1f5bc95b65c23d676e24590bc..43c0c88ef009f8991b078669066d131f164f4796 100644
--- a/media/cdm/aes_decryptor.h
+++ b/media/cdm/aes_decryptor.h
@@ -126,6 +126,9 @@ class MEDIA_EXPORT AesDecryptor : public MediaKeys,
   // the key. Returns NULL if no key is associated with |key_id|.
   DecryptionKey* GetKey(const std::string& key_id) const;
 
+  // Determines if |key_id| is already specified for |session_id|.
+  bool HasKey(const std::string& session_id, const std::string& key_id);
+
   // Deletes all keys associated with |session_id|.
   void DeleteKeysForSession(const std::string& session_id);