Initialize ios/web_view translate with a system-wide URLRequestContext.

ios/web_view/internal/app/web_view_io_thread.mm

+// Copyright 2017 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 "ios/web_view/internal/app/web_view_io_thread.h"
+
+#include "base/memory/ptr_util.h"
+#include "ios/web_view/internal/web_view_network_delegate.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+WebViewIOThread::WebViewIOThread(PrefService* local_state,
+                                 net_log::ChromeNetLog* net_log)
+    : IOThread(local_state, net_log) {}
+
+WebViewIOThread::~WebViewIOThread() = default;
+
+std::unique_ptr<net::NetworkDelegate>
+WebViewIOThread::GetSystemNetworkDelegate() {
+  return base::MakeUnique<ios_web_view::WebViewNetworkDelegate>();
+}