Convert media constants to constexpr.

media/filters/decoder_stream.h

Index: media/filters/decoder_stream.h
diff --git a/media/filters/decoder_stream.h b/media/filters/decoder_stream.h
index 5480373f2a6322c1a53a26b73e1600da1f369ed0..1cf504884cca65fceed2de8f09b394be4fb54b58 100644
--- a/media/filters/decoder_stream.h
+++ b/media/filters/decoder_stream.h
@@ -105,10 +105,10 @@ class MEDIA_EXPORT DecoderStream {
   base::TimeDelta AverageDuration() const;
 
   // Allows callers to register for notification of splice buffers from the
-  // demuxer.  I.e., DecoderBuffer::splice_timestamp() is not kNoTimestamp().
+  // demuxer.  I.e., DecoderBuffer::splice_timestamp() is not kNoTimestamp.
   //
   // The observer will be notified of all buffers with a splice_timestamp() and
-  // the first buffer after which has a splice_timestamp() of kNoTimestamp().
+  // the first buffer after which has a splice_timestamp() of kNoTimestamp.
   typedef base::Callback<void(base::TimeDelta)> SpliceObserverCB;
   void set_splice_observer(const SpliceObserverCB& splice_observer) {
     splice_observer_cb_ = splice_observer;
@@ -225,7 +225,7 @@ class MEDIA_EXPORT DecoderStream {
   ConfigChangeObserverCB config_change_observer_cb_;
 
   // If a splice_timestamp() has been seen, this is true until a
-  // splice_timestamp() of kNoTimestamp() is encountered.
+  // splice_timestamp() of kNoTimestamp is encountered.
   bool active_splice_;
 
   // An end-of-stream buffer has been sent for decoding, no more buffers should