Encrypted Media: Add TRACE_EVENT to trace eme implementation performance.

media/filters/decrypting_video_decoder.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_FILTERS_DECRYPTING_VIDEO_DECODER_H_
 #define MEDIA_FILTERS_DECRYPTING_VIDEO_DECODER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/decryptor.h"
@@ skipping 137 matching lines @@
   // The buffer returned by the demuxer that needs decrypting/decoding.
   scoped_refptr<media::DecoderBuffer> pending_buffer_to_decode_;
 
   // Indicates the situation where new key is added during pending decode
   // (in other words, this variable can only be set in state kPendingDecode).
   // If this variable is true and kNoKey is returned then we need to try
   // decrypting/decoding again in case the newly added key is the correct
   // decryption key.
   bool key_added_while_pending_decode_;
 
+  // A unique ID to trace Decryptor::DecryptAndDecodeVideo() call and the
+  // matching DecryptCB call (in DoDeliverFrame()).
+  uint32 trace_id_;
+
   DISALLOW_COPY_AND_ASSIGN(DecryptingVideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_DECRYPTING_VIDEO_DECODER_H_