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

ios/web_view/internal/app/web_view_io_thread.mm

Index: ios/web_view/internal/app/web_view_io_thread.mm
diff --git a/ios/web_view/internal/app/web_view_io_thread.mm b/ios/web_view/internal/app/web_view_io_thread.mm
new file mode 100644
index 0000000000000000000000000000000000000000..1cd3d6459cbf0a90bc5da72dd4d24f6473d92a5f
--- /dev/null
+++ b/ios/web_view/internal/app/web_view_io_thread.mm
@@ -0,0 +1,31 @@
+// 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
+
+namespace ios_web_view {
+
+WebViewIOThread::WebViewIOThread(PrefService* local_state,
+                                 net_log::ChromeNetLog* net_log)
+    : IOSIOThread(local_state, net_log) {}
+
+WebViewIOThread::~WebViewIOThread() = default;
+
+std::unique_ptr<net::NetworkDelegate>
+WebViewIOThread::CreateSystemNetworkDelegate() {
+  return base::MakeUnique<ios_web_view::WebViewNetworkDelegate>();
+}
+
+std::string WebViewIOThread::GetChannelString() const {
+  return std::string();
+}
+
+}  // namespace ios_web_view