Prepare MediaDrmBridge to work with MediaCodecPlayer

media/cdm/player_tracker_impl.h

Index: media/cdm/player_tracker_impl.h
diff --git a/media/cdm/player_tracker_impl.h b/media/cdm/player_tracker_impl.h
index 6d4cee3b879eec66ecaf868ae6f83096be20b18a..569dd04dbf317f0cd9316133cdc2cff691e82129 100644
--- a/media/cdm/player_tracker_impl.h
+++ b/media/cdm/player_tracker_impl.h
@@ -9,6 +9,7 @@
 
 #include "base/basictypes.h"
 #include "base/callback.h"
+#include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "media/base/media_export.h"
 #include "media/base/player_tracker.h"
@@ -46,6 +47,10 @@ class MEDIA_EXPORT PlayerTrackerImpl : public PlayerTracker {
 
   base::ThreadChecker thread_checker_;
 
+  // Unable to post RegisterPlayer() to another thread since it returns the new
+  // id.
+  base::Lock lock_;
+
   DISALLOW_COPY_AND_ASSIGN(PlayerTrackerImpl);
 };