Bug 1312886: [MSE] P3. Only rely on waiting promise to determine buffering state. r=jwwang

MozReview-Commit-ID: 3HfK8bwqlYM

--HG--
extra : rebase_source : ca44d3ef57165f9764ff57a4932065f19e379e3f

dom/media/MediaDecoderStateMachine.cpp

@@ -1469,14 +1469,11 @@ DecodingState::MaybeStartBuffering()
     return;
   }
 
-  // No more data to download. No need to enter buffering.
-  if (!Resource()->IsExpectingMoreData()) {
-    return;
-  }
-
   bool shouldBuffer;
   if (Reader()->UseBufferingHeuristics()) {
-    shouldBuffer = mMaster->HasLowDecodedData() && mMaster->HasLowBufferedData();
+    shouldBuffer = Resource()->IsExpectingMoreData() &&
+                   mMaster->HasLowDecodedData() &&
+                   mMaster->HasLowBufferedData();
   } else {
     MOZ_ASSERT(Reader()->IsWaitForDataSupported());
     shouldBuffer =