Bug 1290780. Part 3 - Assert IsShutdown() is false in UpdateLogicalPositionInternal(). r=kaku

1. It is called from OnSeekResolved() which asserts !IsShutdown().
2. It is called from UpdateLogicalPosition which asserts !IsShutdown().

MozReview-Commit-ID: J8iuHdUamLS

--HG--
extra : rebase_source : 97215383aa7c409f8b63f5a6726b81df53252227

dom/media/MediaDecoder.cpp

@@ -1342,9 +1342,7 @@ void
 MediaDecoder::UpdateLogicalPositionInternal(MediaDecoderEventVisibility aEventVisibility)
 {
   MOZ_ASSERT(NS_IsMainThread());
-  if (IsShutdown()) {
-    return;
-  }
+  MOZ_ASSERT(!IsShutdown());
 
   double currentPosition = static_cast<double>(CurrentPosition()) / static_cast<double>(USECS_PER_S);
   bool logicalPositionChanged = mLogicalPosition != currentPosition;