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

ios/web_view/internal/web_view_web_client.h

Index: ios/web_view/internal/web_view_web_client.h
diff --git a/ios/web_view/internal/web_view_web_client.h b/ios/web_view/internal/web_view_web_client.h
index b2752b501137f9f7df1679231fb3efc596f90a90..e6048cc8d99c6e052c5972d7d7266aceb257e1e5 100644
--- a/ios/web_view/internal/web_view_web_client.h
+++ b/ios/web_view/internal/web_view_web_client.h
@@ -11,7 +11,6 @@
 #import "ios/web/public/web_client.h"
 
 namespace ios_web_view {
-class WebViewWebMainParts;
 
 // WebView implementation of WebClient.
 class WebViewWebClient : public web::WebClient {
@@ -26,9 +25,6 @@ class WebViewWebClient : public web::WebClient {
   NSString* GetEarlyPageScript(web::BrowserState* browser_state) const override;
 
  private:
-  // The WebMainParts created by |CreateWebMainParts()|.
-  WebViewWebMainParts* web_main_parts_;
-
   DISALLOW_COPY_AND_ASSIGN(WebViewWebClient);
 };