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

ios/web_view/internal/web_view_web_client.mm

Index: ios/web_view/internal/web_view_web_client.mm
diff --git a/ios/web_view/internal/web_view_web_client.mm b/ios/web_view/internal/web_view_web_client.mm
index 319b5e32e24516c62bcb8a0e38e1b5f5d388891c..47184b6f20303c1486051e8571a5a12f57a013f5 100644
--- a/ios/web_view/internal/web_view_web_client.mm
+++ b/ios/web_view/internal/web_view_web_client.mm
@@ -17,13 +17,12 @@
 
 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 {