Introduce DecodeTimestamp class to make it easier to distiguish presentation and decode timestamps.

media/base/stream_parser_unittest.cc

Index: media/base/stream_parser_unittest.cc
diff --git a/media/base/stream_parser_unittest.cc b/media/base/stream_parser_unittest.cc
index 793260ca722306ab27f5adce6674b121bcf390b9..708747c81a16c17d0520f595e691acfa0b2f5063 100644
--- a/media/base/stream_parser_unittest.cc
+++ b/media/base/stream_parser_unittest.cc
@@ -53,7 +53,7 @@ static void GenerateBuffers(const int* decode_timestamps,
         StreamParserBuffer::CopyFrom(kFakeData, sizeof(kFakeData),
                                      true, type, track_id);
     buffer->SetDecodeTimestamp(
-        base::TimeDelta::FromMicroseconds(decode_timestamps[i]));
+        DecodeTimestamp::FromMicroseconds(decode_timestamps[i]));
     queue->push_back(buffer);
   }
 }
@@ -379,4 +379,3 @@ TEST_F(StreamParserTest, MergeBufferQueues_InvalidAppendToExistingMerge) {
 }
 
 }  // namespace media
-