Convert media constants to constexpr.

media/base/decoder_buffer_queue_unittest.cc

Index: media/base/decoder_buffer_queue_unittest.cc
diff --git a/media/base/decoder_buffer_queue_unittest.cc b/media/base/decoder_buffer_queue_unittest.cc
index bc627fdeb70fc66455158b379cb8d89d614d10ec..be2a4b2b3a32cd26e221360b25688ac4607860b9 100644
--- a/media/base/decoder_buffer_queue_unittest.cc
+++ b/media/base/decoder_buffer_queue_unittest.cc
@@ -11,13 +11,13 @@ namespace media {
 
 static base::TimeDelta ToTimeDelta(int seconds) {
   if (seconds < 0)
-    return kNoTimestamp();
+    return kNoTimestamp;
   return base::TimeDelta::FromSeconds(seconds);
 }
 
 // Helper to create buffers with specified timestamp in seconds.
 //
-// Negative numbers will be converted to kNoTimestamp();
+// Negative numbers will be converted to kNoTimestamp;
 static scoped_refptr<DecoderBuffer> CreateBuffer(int timestamp) {
   scoped_refptr<DecoderBuffer> buffer = new DecoderBuffer(0);
   buffer->set_timestamp(ToTimeDelta(timestamp));