Implement ISO BMFF support in Media Source.

media/mp4/track_run_iterator.cc

Index: media/mp4/track_run_iterator.cc
diff --git a/media/mp4/track_run_iterator.cc b/media/mp4/track_run_iterator.cc
index 440ea06325e33e94022067cf24fca955fcff0469..8ec05e21099a551c34832454f23524c83e5d95f4 100644
--- a/media/mp4/track_run_iterator.cc
+++ b/media/mp4/track_run_iterator.cc
@@ -13,7 +13,8 @@ namespace media {
 namespace mp4 {
 
 base::TimeDelta TimeDeltaFromFrac(int64 numer, uint64 denom) {
-  DCHECK_LT(std::abs(numer), kint64max / base::Time::kMicrosecondsPerSecond);
+  DCHECK_LT((numer > 0 ? numer : -numer),
+            kint64max / base::Time::kMicrosecondsPerSecond);
   return base::TimeDelta::FromMicroseconds(
         base::Time::kMicrosecondsPerSecond * numer / denom);
 }