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

ios/web_view/internal/web_view_web_main_parts.h

 // Copyright 2014 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_WEB_VIEW_WEB_MAIN_PARTS_H_
 #define IOS_WEB_VIEW_INTERNAL_WEB_VIEW_WEB_MAIN_PARTS_H_
 
 #include <memory>
 
+#include "base/macros.h"
 #include "ios/web/public/app/web_main_parts.h"
 
-@protocol CWVDelegate;
-
 namespace ios_web_view {
 
 // WebView implementation of WebMainParts.
 class WebViewWebMainParts : public web::WebMainParts {
  public:
   WebViewWebMainParts();
   ~WebViewWebMainParts() override;
 
-  // WebMainParts implementation.
+ private:
+  // web::WebMainParts implementation.
+  void PreMainMessageLoopStart() override;
+  void PreCreateThreads() override;
   void PreMainMessageLoopRun() override;
+  void PostMainMessageLoopRun() override;
+  void PostDestroyThreads() override;
+
+  DISALLOW_COPY_AND_ASSIGN(WebViewWebMainParts);
 };
 
 }  // namespace ios_web_view
 
 #endif  // IOS_WEB_VIEW_INTERNAL_WEB_VIEW_WEB_MAIN_PARTS_H_