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

content/common/throttling_url_loader.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_COMMON_THROTTLING_URL_LOADER_H_
 #define CONTENT_COMMON_THROTTLING_URL_LOADER_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 52 matching lines @@
       mojom::URLLoaderClient* client,
       const net::NetworkTrafficAnnotationTag& traffic_annotation,
       scoped_refptr<base::SingleThreadTaskRunner> task_runner =
           base::ThreadTaskRunnerHandle::Get());
 
   ~ThrottlingURLLoader() override;
 
   void FollowRedirect();
   void SetPriority(net::RequestPriority priority, int32_t intra_priority_value);
 
+  // Disconnects the client connection and releases the URLLoader.
+  void DisconnectClient();
+
  private:
   ThrottlingURLLoader(
       std::vector<std::unique_ptr<URLLoaderThrottle>> throttles,
       mojom::URLLoaderClient* client,
       const net::NetworkTrafficAnnotationTag& traffic_annotation);
 
   // Either of the two sets of arguments below is valid but not both:
   // - |factory|, |routing_id|, |request_id| and |options|;
   // - |start_loader_callback|.
   void Start(mojom::URLLoaderFactory* factory,
@@ skipping 32 matching lines @@
   void CancelWithError(int error_code) override;
   void Resume() override;
 
   enum DeferredStage {
     DEFERRED_NONE,
     DEFERRED_START,
     DEFERRED_REDIRECT,
     DEFERRED_RESPONSE
   };
   DeferredStage deferred_stage_ = DEFERRED_NONE;
-  bool cancelled_by_throttle_ = false;
+  bool loader_cancelled_ = false;
 
   std::unique_ptr<URLLoaderThrottle> throttle_;
 
   mojom::URLLoaderClient* forwarding_client_;
   mojo::Binding<mojom::URLLoaderClient> client_binding_;
 
   mojom::URLLoaderPtr url_loader_;
 
   struct StartInfo {
     StartInfo(mojom::URLLoaderFactory* in_url_loader_factory,
@@ skipping 55 matching lines @@
   std::unique_ptr<PriorityInfo> priority_info_;
 
   const net::NetworkTrafficAnnotationTag traffic_annotation_;
 
   DISALLOW_COPY_AND_ASSIGN(ThrottlingURLLoader);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_THROTTLING_URL_LOADER_H_