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

content/browser/loader/url_loader_request_handler.cc

 // 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.
 
 #include "content/browser/loader/url_loader_request_handler.h"
 
 namespace content {
 
 mojom::URLLoaderFactoryPtr
 URLLoaderRequestHandler::MaybeCreateSubresourceFactory() {
   return nullptr;
 }
 
+bool URLLoaderRequestHandler::MaybeGetFallbackForResponse(
+    const ResourceResponseHead& response,
+    mojom::URLLoaderClientPtr* client,
+    mojom::URLLoaderRequest* request) {
+  return false;
+}
+
+bool URLLoaderRequestHandler::MaybeGetFallbackForRedirect(
+    const ResourceResponseHead& response,
+    const net::RedirectInfo& redirect_info,
+    mojom::URLLoaderClientPtr* client,
+    mojom::URLLoaderRequest* request) {
+  return false;
+}
+
 }  // namespace content