[Fetch API] Introduce BytesConsumer

third_party/WebKit/Source/modules/fetch/BytesConsumer.cpp

+// Copyright 2016 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 "modules/fetch/BytesConsumer.h"
+
+#include <algorithm>
+#include <string.h>
+
+namespace blink {
+
+BytesConsumer::Result BytesConsumer::read(char* buffer, size_t size, size_t* readSize)
+{
+    *readSize = 0;
+    const char* src = nullptr;
+    size_t available;
+    Result r = beginRead(&src, &available);
+    if (r != Result::Ok)
+        return r;
+    *readSize = std::min(available, size);
+    memcpy(buffer, src, *readSize);
+    return endRead(*readSize);
+}
+
+} // namespace blink