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diff --git a/js/src/builtin/streams/QueueWithSizes.cpp b/js/src/builtin/streams/QueueWithSizes.cpp
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+++ b/js/src/builtin/streams/QueueWithSizes.cpp
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Queue-with-sizes operations. */
+
+#include "builtin/streams/QueueWithSizes-inl.h"
+
+#include "mozilla/Assertions.h"     // MOZ_ASSERT
+#include "mozilla/Attributes.h"     // MOZ_MUST_USE
+#include "mozilla/FloatingPoint.h"  // mozilla::Is{Infinite,NaN}
+
+#include "jsapi.h"  // JS_ReportErrorNumberASCII
+
+#include "builtin/streams/StreamController.h"  // js::StreamController
+#include "js/Class.h"                 // JSClass, JSCLASS_HAS_RESERVED_SLOTS
+#include "js/Conversions.h"           // JS::ToNumber
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/RootingAPI.h"            // JS::Rooted
+#include "js/Value.h"                 // JS::Value, JS::{Number,Object}Value
+#include "vm/Compartment.h"           // JSCompartment
+#include "vm/JSContext.h"             // JSContext
+#include "vm/List.h"                  // js::ListObject
+#include "vm/NativeObject.h"          // js::NativeObject
+
+#include "vm/Compartment-inl.h"  // JSCompartment::wrap
+#include "vm/JSContext-inl.h"    // JSContext::check
+#include "vm/JSObject-inl.h"     // js::NewBuiltinClassInstance
+#include "vm/List-inl.h"   // js::ListObject::*, js::StoreNewListInFixedSlot
+#include "vm/Realm-inl.h"  // js::AutoRealm
+
+using JS::Handle;
+using JS::MutableHandle;
+using JS::NumberValue;
+using JS::ObjectValue;
+using JS::Rooted;
+using JS::ToNumber;
+using JS::Value;
+
+/*** 6.2. Queue-with-sizes operations ***************************************/
+
+/**
+ * Streams spec, 6.2.1. DequeueValue ( container ) nothrow
+ */
+MOZ_MUST_USE bool js::DequeueValue(JSContext* cx,
+                                   Handle<StreamController*> unwrappedContainer,
+                                   MutableHandle<Value> chunk) {
+  // Step 1: Assert: container has [[queue]] and [[queueTotalSize]] internal
+  //         slots (implicit).
+  // Step 2: Assert: queue is not empty.
+  Rooted<ListObject*> unwrappedQueue(cx, unwrappedContainer->queue());
+
+  // Step 3. Let pair be the first element of queue.
+  double chunkSize = detail::QueueFirstSize(unwrappedQueue);
+  chunk.set(detail::QueueFirstValue(unwrappedQueue));
+
+  // Step 4. Remove pair from queue, shifting all other elements downward
+  //         (so that the second becomes the first, and so on).
+  detail::QueueRemoveFirstValueAndSize(unwrappedQueue, cx);
+
+  // Step 5: Set container.[[queueTotalSize]] to
+  //         container.[[queueTotalSize]] − pair.[[size]].
+  // Step 6: If container.[[queueTotalSize]] < 0, set
+  //         container.[[queueTotalSize]] to 0.
+  //         (This can occur due to rounding errors.)
+  double totalSize = unwrappedContainer->queueTotalSize();
+  totalSize -= chunkSize;
+  if (totalSize < 0) {
+    totalSize = 0;
+  }
+  unwrappedContainer->setQueueTotalSize(totalSize);
+
+  // Step 7: Return pair.[[value]].
+  return cx->compartment()->wrap(cx, chunk);
+}
+
+void js::DequeueValue(StreamController* unwrappedContainer, JSContext* cx) {
+  // Step 1: Assert: container has [[queue]] and [[queueTotalSize]] internal
+  //         slots (implicit).
+  // Step 2: Assert: queue is not empty.
+  ListObject* unwrappedQueue = unwrappedContainer->queue();
+
+  // Step 3. Let pair be the first element of queue.
+  // (The value is being discarded, so all we must extract is the size.)
+  double chunkSize = detail::QueueFirstSize(unwrappedQueue);
+
+  // Step 4. Remove pair from queue, shifting all other elements downward
+  //         (so that the second becomes the first, and so on).
+  detail::QueueRemoveFirstValueAndSize(unwrappedQueue, cx);
+
+  // Step 5: Set container.[[queueTotalSize]] to
+  //         container.[[queueTotalSize]] − pair.[[size]].
+  // Step 6: If container.[[queueTotalSize]] < 0, set
+  //         container.[[queueTotalSize]] to 0.
+  //         (This can occur due to rounding errors.)
+  double totalSize = unwrappedContainer->queueTotalSize();
+  totalSize -= chunkSize;
+  if (totalSize < 0) {
+    totalSize = 0;
+  }
+  unwrappedContainer->setQueueTotalSize(totalSize);
+
+  // Step 7: Return pair.[[value]].  (omitted because not used)
+}
+
+/**
+ * Streams spec, 6.2.2. EnqueueValueWithSize ( container, value, size ) throws
+ */
+MOZ_MUST_USE bool js::EnqueueValueWithSize(
+    JSContext* cx, Handle<StreamController*> unwrappedContainer,
+    Handle<Value> value, Handle<Value> sizeVal) {
+  cx->check(value, sizeVal);
+
+  // Step 1: Assert: container has [[queue]] and [[queueTotalSize]] internal
+  //         slots (implicit).
+  // Step 2: Let size be ? ToNumber(size).
+  double size;
+  if (!ToNumber(cx, sizeVal, &size)) {
+    return false;
+  }
+
+  // Step 3: If ! IsFiniteNonNegativeNumber(size) is false, throw a RangeError
+  //         exception.
+  if (size < 0 || mozilla::IsNaN(size) || mozilla::IsInfinite(size)) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_NUMBER_MUST_BE_FINITE_NON_NEGATIVE, "size");
+    return false;
+  }
+
+  // Step 4: Append Record {[[value]]: value, [[size]]: size} as the last
+  //         element of container.[[queue]].
+  {
+    AutoRealm ar(cx, unwrappedContainer);
+    Rooted<ListObject*> unwrappedQueue(cx, unwrappedContainer->queue());
+    Rooted<Value> wrappedVal(cx, value);
+    if (!cx->compartment()->wrap(cx, &wrappedVal)) {
+      return false;
+    }
+
+    if (!detail::QueueAppendValueAndSize(cx, unwrappedQueue, wrappedVal,
+                                         size)) {
+      return false;
+    }
+  }
+
+  // Step 5: Set container.[[queueTotalSize]] to
+  //         container.[[queueTotalSize]] + size.
+  unwrappedContainer->setQueueTotalSize(unwrappedContainer->queueTotalSize() +
+                                        size);
+
+  return true;
+}
+
+/**
+ * Streams spec, 6.2.4. ResetQueue ( container ) nothrow
+ */
+MOZ_MUST_USE bool js::ResetQueue(JSContext* cx,
+                                 Handle<StreamController*> unwrappedContainer) {
+  // Step 1: Assert: container has [[queue]] and [[queueTotalSize]] internal
+  //         slots (implicit).
+  // Step 2: Set container.[[queue]] to a new empty List.
+  if (!StoreNewListInFixedSlot(cx, unwrappedContainer,
+                               StreamController::Slot_Queue)) {
+    return false;
+  }
+
+  // Step 3: Set container.[[queueTotalSize]] to 0.
+  unwrappedContainer->setQueueTotalSize(0);
+
+  return true;
+}