Remove implicit conversions from scoped_refptr to T* in android_webview/

android_webview/native/aw_contents_client_bridge.cc

Index: android_webview/native/aw_contents_client_bridge.cc
diff --git a/android_webview/native/aw_contents_client_bridge.cc b/android_webview/native/aw_contents_client_bridge.cc
index f5bccdffd86bc6a5b25f4c1c3d1df2e9796dc373..9d6860378e57ef682ec8a46d01ff367b9f225252 100644
--- a/android_webview/native/aw_contents_client_bridge.cc
+++ b/android_webview/native/aw_contents_client_bridge.cc
@@ -379,7 +379,7 @@ void AwContentsClientBridge::HandleErrorInClientCertificateResponse(
     int request_id) {
   SelectCertificateCallback* callback =
       pending_client_cert_request_callbacks_.Lookup(request_id);
-  callback->Run(scoped_refptr<net::X509Certificate>());
+  callback->Run(nullptr);
   pending_client_cert_request_callbacks_.Remove(request_id);
 }