AesDecryptor callbacks now used in a thread-safe manner

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 a72674c102da801ee351a6c0ef44fc65dd10d291..ac45e68aa9cb1155a2cc11a9c4f2b6dcaa2f6fb9 100644
--- a/media/cdm/aes_decryptor.h
+++ b/media/cdm/aes_decryptor.h
@@ -135,6 +135,10 @@ class MEDIA_EXPORT AesDecryptor : public MediaKeys, public Decryptor {
   NewKeyCB new_audio_key_cb_;
   NewKeyCB new_video_key_cb_;
 
+  // Protect |new_audio_key_cb_| and |new_video_key_cb_| as they are set on the
+  // main thread but called on the media thread.
+  mutable base::Lock new_key_cb_lock_;
+
   DISALLOW_COPY_AND_ASSIGN(AesDecryptor);
 };