Bug 1207198: P2. Defer dormant request while ReadMetadata is pending in MDSM. r=sotaro

dom/media/MediaDecoderStateMachine.cpp

@@ -1246,6 +1246,18 @@ MediaDecoderStateMachine::SetDormant(bool aDormant)
     return;
   }
 
+  if (mMetadataRequest.Exists()) {
+    if (mPendingDormant && mPendingDormant.ref() != aDormant && !aDormant) {
+      // We already have a dormant request pending; the new request would have
+      // resumed from dormant, we can just cancel any pending dormant requests.
+      mPendingDormant.reset();
+    } else {
+      mPendingDormant = Some(aDormant);
+    }
+    return;
+  }
+  mPendingDormant.reset();
+
   DECODER_LOG("SetDormant=%d", aDormant);
 
   if (aDormant) {
@@ -1906,6 +1918,11 @@ MediaDecoderStateMachine::OnMetadataRead(MetadataHolder* aMetadata)
   MOZ_ASSERT(mState == DECODER_STATE_DECODING_METADATA);
   mMetadataRequest.Complete();
 
+  if (mPendingDormant) {
+    SetDormant(mPendingDormant.ref());
+    return;
+  }
+
   // Set mode to PLAYBACK after reading metadata.
   mResource->SetReadMode(MediaCacheStream::MODE_PLAYBACK);
   mDecoder->DispatchSetMediaSeekable(mReader->IsMediaSeekable());

dom/media/MediaDecoderStateMachine.h

@@ -1086,6 +1086,9 @@ private:
   // been written to the MediaStream.
   Watchable<bool> mAudioCompleted;
 
+  // Set if MDSM receives dormant request during reading metadata.
+  Maybe<bool> mPendingDormant;
+
   // Flag whether we notify metadata before decoding the first frame or after.
   //
   // Note that the odd semantics here are designed to replicate the current