Convert media constants to constexpr.

media/formats/mp2t/es_parser_adts.cc

Index: media/formats/mp2t/es_parser_adts.cc
diff --git a/media/formats/mp2t/es_parser_adts.cc b/media/formats/mp2t/es_parser_adts.cc
index cd8d3886d0593a558d01c49d2b5fb0d384d90ca2..6ab784574c168a14dbe81fb4c65a4dc680a30bea 100644
--- a/media/formats/mp2t/es_parser_adts.cc
+++ b/media/formats/mp2t/es_parser_adts.cc
@@ -129,10 +129,10 @@ bool EsParserAdts::ParseFromEsQueue() {
     // Get the PTS & the duration of this access unit.
     TimingDesc current_timing_desc =
         GetTimingDescriptor(adts_frame.queue_offset);
-    if (current_timing_desc.pts != kNoTimestamp())
+    if (current_timing_desc.pts != kNoTimestamp)
       audio_timestamp_helper_->SetBaseTimestamp(current_timing_desc.pts);
 
-    if (audio_timestamp_helper_->base_timestamp() == kNoTimestamp()) {
+    if (audio_timestamp_helper_->base_timestamp() == kNoTimestamp) {
       DVLOG(1) << "Skipping audio frame with unknown timestamp";
       SkipAdtsFrame(adts_frame);
       continue;
@@ -196,7 +196,7 @@ bool EsParserAdts::UpdateAudioConfiguration(const uint8_t* adts_header) {
 
     // Reset the timestamp helper to use a new time scale.
     if (audio_timestamp_helper_ &&
-        audio_timestamp_helper_->base_timestamp() != kNoTimestamp()) {
+        audio_timestamp_helper_->base_timestamp() != kNoTimestamp) {
       base::TimeDelta base_timestamp = audio_timestamp_helper_->GetTimestamp();
       audio_timestamp_helper_.reset(new AudioTimestampHelper(orig_sample_rate));
       audio_timestamp_helper_->SetBaseTimestamp(base_timestamp);