Verify EME calls made on same thread

media/base/cdm_promise_adapter.h

Index: media/base/cdm_promise_adapter.h
diff --git a/media/base/cdm_promise_adapter.h b/media/base/cdm_promise_adapter.h
index b078c0dd0a5393ba22174cc5e34a1161fad19d06..b6d5a89be5be717dfd61760c98b21cc1c32a6745 100644
--- a/media/base/cdm_promise_adapter.h
+++ b/media/base/cdm_promise_adapter.h
@@ -9,6 +9,7 @@
 #include "base/containers/scoped_ptr_hash_map.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "media/base/cdm_promise.h"
 #include "media/base/media_export.h"
 
@@ -51,6 +52,7 @@ class MEDIA_EXPORT CdmPromiseAdapter {
   uint32_t next_promise_id_;
   PromiseMap promises_;
 
+  base::ThreadChecker thread_checker_;
   DISALLOW_COPY_AND_ASSIGN(CdmPromiseAdapter);
 };