Bug 1429009. P2 - remove unnecessary AbstractThread::AutoEnter. r=bechen,gerald

It is not needed since we are already in the right context.

MozReview-Commit-ID: 6QXxLMQHavv

--HG--
extra : rebase_source : d7a80d3e3d6583bd1732a4048f40576603e83872
extra : source : d700cc52ce2a50a784601f7cff7f63eaff3efced

dom/media/ChannelMediaDecoder.cpp

@@ -439,7 +439,6 @@ ChannelMediaDecoder::DownloadProgressed()
         mCanPlayThrough = aStats.CanPlayThrough();
         GetStateMachine()->DispatchCanPlayThrough(mCanPlayThrough);
         mResource->ThrottleReadahead(ShouldThrottleDownload(aStats));
-        AbstractThread::AutoEnter context(AbstractMainThread());
         // Update readyState since mCanPlayThrough might have changed.
         GetOwner()->UpdateReadyState();
       },