Add methods for creating V8 extras-based ReadableStreams from C++

Source/core/streams/ReadableStream2.cpp

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/streams/ReadableStream2.h"
+
+#include "bindings/core/v8/ToV8.h"
+#include "bindings/core/v8/V8RecursionScope.h"
+
+namespace blink {
+
+ReadableStream2::ReadableStream2(ScriptState* scriptState, UnderlyingSourceBase* underlyingSource, QueuingStrategyBase* strategy)
+{
+    ScriptState::Scope scope(scriptState);
+
+    auto global = scriptState->context()->Global();
+    auto isolate = scriptState->isolate();
+
+    auto jsUnderlyingSource = toV8(underlyingSource, global, isolate);
+    auto jsStrategy = toV8(strategy, global, isolate);
+
+    auto sentinel = scriptState->getFromExtrasExports("createWithExternalControllerSentinel").v8Value();
+    auto constructor = scriptState->getFromExtrasExports("ReadableStream").v8Value().As<v8::Function>();
+
+    v8::Local<v8::Value> args[] = { jsUnderlyingSource, jsStrategy, sentinel };
+
+    V8RecursionScope::MicrotaskSuppression mtsScope(isolate);
+    auto jsStream = constructor->NewInstance(arraysize(args), args);
+
+    m_stream = ScriptValue(scriptState, jsStream);
+}
+
+bool ReadableStream2::isLocked() const
+{
+    ScriptState::Scope scope(m_stream.scriptState());
+    auto func = m_stream.scriptState()->getFromExtrasExports("IsReadableStreamLocked").v8Value().As<v8::Function>();
+
+    auto undefined = v8::Undefined(m_stream.isolate());
+    v8::Local<v8::Value> args[] = { m_stream.v8Value() };
+    return func->Call(undefined, arraysize(args), args).As<v8::Boolean>()->Value();
+}
+
+}