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

ios/web_view/internal/web_view_web_client.mm

 // 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.
 
 #import "ios/web_view/internal/web_view_web_client.h"
 
 #include "base/strings/sys_string_conversions.h"
 #include "ios/web/public/user_agent.h"
 #include "ios/web_view/internal/web_view_browser_state.h"
 #import "ios/web_view/internal/web_view_early_page_script_provider.h"
 #import "ios/web_view/internal/web_view_web_main_parts.h"
 #include "ios/web_view/public/cwv_web_view.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace ios_web_view {
 
-WebViewWebClient::WebViewWebClient() : web_main_parts_(nullptr) {}
+WebViewWebClient::WebViewWebClient() {}
 
 WebViewWebClient::~WebViewWebClient() = default;
 
 web::WebMainParts* WebViewWebClient::CreateWebMainParts() {
-  web_main_parts_ = new WebViewWebMainParts();
-  return web_main_parts_;
+  return new WebViewWebMainParts();
 }
 
 std::string WebViewWebClient::GetProduct() const {
   return base::SysNSStringToUTF8([CWVWebView userAgentProduct]);
 }
 
 std::string WebViewWebClient::GetUserAgent(web::UserAgentType type) const {
   return web::BuildUserAgentFromProduct(GetProduct());
 }
 
 NSString* WebViewWebClient::GetEarlyPageScript(
     web::BrowserState* browser_state) const {
   return WebViewEarlyPageScriptProvider::FromBrowserState(browser_state)
       .GetScript();
 }
 
 }  // namespace ios_web_view