Initializes some uninitialized class members of TrackRunIterator.

Bug: none
Change-Id: I3636b34d6f87f9db732f1263cc3f2eddeb39335f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1670527Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671896}

media/formats/mp4/track_run_iterator.cc

@@ -119,7 +119,11 @@ DecodeTimestamp DecodeTimestampFromRational(int64_t numer, int64_t denom) {
 }
 
 TrackRunIterator::TrackRunIterator(const Movie* moov, MediaLog* media_log)
-    : moov_(moov), media_log_(media_log), sample_offset_(0) {
+    : moov_(moov),
+      media_log_(media_log),
+      sample_dts_(0),
+      sample_cts_(0),
+      sample_offset_(0) {
   CHECK(moov);
 }