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

media/formats/mp2t/es_parser_h264.h

Index: media/formats/mp2t/es_parser_h264.h
diff --git a/media/formats/mp2t/es_parser_h264.h b/media/formats/mp2t/es_parser_h264.h
index 674b2c650a9c5be50e63a6c5a802806ba58c5c91..82499f5ec530ecb86812426fb8206894f0391e62 100644
--- a/media/formats/mp2t/es_parser_h264.h
+++ b/media/formats/mp2t/es_parser_h264.h
@@ -43,13 +43,13 @@ class MEDIA_EXPORT EsParserH264 : NON_EXPORTED_BASE(public EsParser) {
   // EsParser implementation.
   virtual bool Parse(const uint8* buf, int size,
                      base::TimeDelta pts,
-                     base::TimeDelta dts) OVERRIDE;
+                     DecodeTimestamp dts) OVERRIDE;
   virtual void Flush() OVERRIDE;
   virtual void Reset() OVERRIDE;
 
  private:
   struct TimingDesc {
-    base::TimeDelta dts;
+    DecodeTimestamp dts;
     base::TimeDelta pts;
   };
 
@@ -96,4 +96,3 @@ class MEDIA_EXPORT EsParserH264 : NON_EXPORTED_BASE(public EsParser) {
 }  // namespace media
 
 #endif
-