Bug 1382303 - P3. Reduce enough data threadhold to 10s. r=jwwang

We waited 30s until we changed readyState to HAVE_ENOUGH_DATA this would cause autoplay media element to start rather late. In particular with live stream. 10s is typically enough ahead time to start playback.

MozReview-Commit-ID: LJvY8cQYfwZ

--HG--
extra : rebase_source : 4c75326891ba4e9317c432ea7074eb033a77b300

dom/media/mediasource/MediaSourceDecoder.cpp

@@ -306,12 +306,12 @@ MediaSourceDecoder::CanPlayThrough()
   } else if (duration <= currentPosition) {
     return true;
   }
-  // If we have data up to the mediasource's duration or 30s ahead, we can
+  // If we have data up to the mediasource's duration or 10s ahead, we can
   // assume that we can play without interruption.
   TimeIntervals buffered = GetBuffered();
   buffered.SetFuzz(MediaSourceDemuxer::EOS_FUZZ / 2);
   TimeUnit timeAhead =
-    std::min(duration, currentPosition + TimeUnit::FromSeconds(30));
+    std::min(duration, currentPosition + TimeUnit::FromSeconds(10));
   TimeInterval interval(currentPosition, timeAhead);
   return buffered.ContainsStrict(ClampIntervalToEnd(interval));
 }