Encrypted Media: Add TRACE_EVENT to trace eme implementation performance.

media/filters/decrypting_video_decoder.h

Index: media/filters/decrypting_video_decoder.h
diff --git a/media/filters/decrypting_video_decoder.h b/media/filters/decrypting_video_decoder.h
index 900b0bb3db9e8a1c74b620bea286329df2d5fc85..ba63cde959ed619757c7ea58f87dc980efd140c3 100644
--- a/media/filters/decrypting_video_decoder.h
+++ b/media/filters/decrypting_video_decoder.h
@@ -155,6 +155,10 @@ class MEDIA_EXPORT DecryptingVideoDecoder : public VideoDecoder {
   // decryption key.
   bool key_added_while_pending_decode_;
 
+  // A unique ID to trace Decryptor::DecryptAndDecodeVideo() call and the
+  // matching DecryptCB call (in DoDeliverFrame()).
+  unsigned int trace_id_;

[scherkus (not reviewing), 2012/11/01 22:22:36]

do we need unsigned?

[xhwang, 2012/11/02 01:33:54]

I am super paranoid, about what if the trace_id_ overflows.  Overflowing "int"
is undefined behavior. "unsigned" gives me peace of mind.

+
   DISALLOW_COPY_AND_ASSIGN(DecryptingVideoDecoder);
 };