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

ios/web_view/internal/app/web_view_io_thread.h

Index: ios/web_view/internal/app/web_view_io_thread.h
diff --git a/ios/web_view/internal/app/web_view_io_thread.h b/ios/web_view/internal/app/web_view_io_thread.h
new file mode 100644
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+++ b/ios/web_view/internal/app/web_view_io_thread.h
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+// 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.
+
+#ifndef IOS_WEB_VIEW_INTERNAL_APP_WEB_VIEW_IO_THREAD_H_
+#define IOS_WEB_VIEW_INTERNAL_APP_WEB_VIEW_IO_THREAD_H_
+
+#include <memory>
+
+#include "ios/components/io_thread/io_thread.h"
+
+class PrefService;
+
+namespace net_log {
+class ChromeNetLog;
+}  // namespace net_log
+
+// Contains state associated with, initialized and cleaned up on, and
+// primarily used on, the IO thread.
+class WebViewIOThread : public io_thread::IOThread {
+ public:
+  WebViewIOThread(PrefService* local_state, net_log::ChromeNetLog* net_log);
+  ~WebViewIOThread() override;
+
+ protected:
+  // The "system" NetworkDelegate, used for BrowserState-agnostic network
+  // events.
+  std::unique_ptr<net::NetworkDelegate> GetSystemNetworkDelegate() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WebViewIOThread);
+};
+
+#endif  // IOS_WEB_VIEW_INTERNAL_APP_WEB_VIEW_IO_THREAD_H_