Fix UMA metrics for MediaSourcePlayer.

media/base/android/media_statistics.cc

Index: media/base/android/media_statistics.cc
diff --git a/media/base/android/media_statistics.cc b/media/base/android/media_statistics.cc
index 19c0298e6ce0e7aa0ddac068410dca684edb8812..d3d36bb4ebed42ddd97d940135672f7b2f43b340 100644
--- a/media/base/android/media_statistics.cc
+++ b/media/base/android/media_statistics.cc
@@ -53,6 +53,12 @@ void MediaStatistics::StopAndReport(base::TimeDelta current_playback_time) {
   if (start_time_ == kNoTimestamp())
     return;  // skip if there was no prior Start().
 
+  if (current_playback_time == kNoTimestamp()) {
+    // Cancel the start event and skip if current time is unknown.
+    start_time_ = kNoTimestamp();
+    return;
+  }
+
   base::TimeDelta duration = current_playback_time - start_time_;
 
   // Reset start time.