Add support for fallback content for the frame. This includes main and subframes.

content/common/throttling_url_loader.cc

Index: content/common/throttling_url_loader.cc
diff --git a/content/common/throttling_url_loader.cc b/content/common/throttling_url_loader.cc
index 8843606cad75c5e12fe50d0fb1bfc8641d7046ed..486a8c9e7db7af5291a4c09717af622867d893d5 100644
--- a/content/common/throttling_url_loader.cc
+++ b/content/common/throttling_url_loader.cc
@@ -103,6 +103,11 @@ void ThrottlingURLLoader::SetPriority(net::RequestPriority priority,
   url_loader_->SetPriority(priority, intra_priority_value);
 }
 
+void ThrottlingURLLoader::DisconnectClient() {
+  client_binding_.Close();
+  url_loader_ = nullptr;
+}
+
 ThrottlingURLLoader::ThrottlingURLLoader(
     std::vector<std::unique_ptr<URLLoaderThrottle>> throttles,
     mojom::URLLoaderClient* client,
@@ -295,9 +300,7 @@ void ThrottlingURLLoader::CancelWithError(int error_code) {
   request_complete_data.completion_time = base::TimeTicks::Now();
 
   deferred_stage_ = DEFERRED_NONE;
-  client_binding_.Close();
-  url_loader_ = nullptr;
-
+  DisconnectClient();
   forwarding_client_->OnComplete(request_complete_data);
 }