Return a specific error code for unknown URL schemes.

content/browser/renderer_host/resource_dispatcher_host.cc

Index: content/browser/renderer_host/resource_dispatcher_host.cc
diff --git a/content/browser/renderer_host/resource_dispatcher_host.cc b/content/browser/renderer_host/resource_dispatcher_host.cc
index 4a6a0577603bcc8e7fc368433a0248a0c232656f..ac31353b03d09c62fa8868cc8fc83b7b8874e5fa 100644
--- a/content/browser/renderer_host/resource_dispatcher_host.cc
+++ b/content/browser/renderer_host/resource_dispatcher_host.cc
@@ -388,7 +388,8 @@ bool ResourceDispatcherHost::HandleExternalProtocol(
 
   handler->OnResponseCompleted(
       request_id,
-      net::URLRequestStatus(net::URLRequestStatus::FAILED, net::ERR_ABORTED),
+      net::URLRequestStatus(net::URLRequestStatus::FAILED,
+                            net::ERR_UNKNOWN_URL_SCHEME),
       std::string());  // No security info necessary.
   return true;
 }