Bug 1605699 - part1 : add an assertion to ensure 'GetSample()' always return a valid sample. r=bryce

Differential Revision: https://phabricator.services.mozilla.com/D58392

--HG--
extra : moz-landing-system : lando

dom/media/mediasource/TrackBuffersManager.cpp

@@ -2624,6 +2624,7 @@ const MediaRawData* TrackBuffersManager::GetSample(TrackInfo::TrackType aTrack,
   const RefPtr<MediaRawData>& sample = track[aIndex];
   if (!aIndex || sample->mTimecode <= aExpectedDts + aFuzz ||
       sample->mTime <= aExpectedPts + aFuzz) {
+    MOZ_DIAGNOSTIC_ASSERT(sample->HasValidTime());
     return sample;
   }