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

ios/web_view/internal/web_view_web_main_parts.h

Index: ios/web_view/internal/web_view_web_main_parts.h
diff --git a/ios/web_view/internal/web_view_web_main_parts.h b/ios/web_view/internal/web_view_web_main_parts.h
index 10f02796fb6fad5b8a0bfc709ff76e3faa4a94a8..31bb1bb46afef30707cb8f7b3d813c2b36481a3d 100644
--- a/ios/web_view/internal/web_view_web_main_parts.h
+++ b/ios/web_view/internal/web_view_web_main_parts.h
@@ -7,10 +7,9 @@
 
 #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.
@@ -19,8 +18,15 @@ class WebViewWebMainParts : public web::WebMainParts {
   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