Assert there are no pending reads when releasing lock in tee()

Author: MattiasBuelens

Diff for: reference-implementation/lib/abstract-ops/readable-streams.js

@@ -499,6 +499,7 @@ function ReadableByteStreamTee(stream) {
 
   function pullWithDefaultReader() {
     if (ReadableStreamBYOBReader.isImpl(reader)) {
+      assert(reader._readIntoRequests.length === 0);
       ReadableStreamBYOBReaderRelease(reader);
 
       reader = AcquireReadableStreamDefaultReader(stream);
@@ -569,6 +570,7 @@ function ReadableByteStreamTee(stream) {
 
   function pullWithBYOBReader(view, forBranch2) {
     if (ReadableStreamDefaultReader.isImpl(reader)) {
+      assert(reader._readRequests.length === 0);
       ReadableStreamDefaultReaderRelease(reader);
 
       reader = AcquireReadableStreamBYOBReader(stream);