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

content/browser/appcache/appcache_url_loader_job.cc

Index: content/browser/appcache/appcache_url_loader_job.cc
diff --git a/content/browser/appcache/appcache_url_loader_job.cc b/content/browser/appcache/appcache_url_loader_job.cc
index c6594d1595d35c3b0709549f105f02075c5c6c8a..5679b7a19128911a16a88b612aca9b68c35e9fd6 100644
--- a/content/browser/appcache/appcache_url_loader_job.cc
+++ b/content/browser/appcache/appcache_url_loader_job.cc
@@ -223,16 +223,20 @@ void AppCacheURLLoaderJob::SetSubresourceLoadInfo(
   default_url_loader_factory_getter_ = default_url_loader;
 }
 
-void AppCacheURLLoaderJob::Start(mojom::URLLoaderRequest request,
-                                 mojom::URLLoaderClientPtr client) {
+void AppCacheURLLoaderJob::BindRequest(mojom::URLLoaderClientPtr client,
+                                       mojom::URLLoaderRequest request) {
   DCHECK(!binding_.is_bound());
   binding_.Bind(std::move(request));
 
+  client_ = std::move(client);
+
   binding_.set_connection_error_handler(base::Bind(
       &AppCacheURLLoaderJob::OnConnectionError, StaticAsWeakPtr(this)));
+}
 
-  client_ = std::move(client);
-
+void AppCacheURLLoaderJob::Start(mojom::URLLoaderRequest request,
+                                 mojom::URLLoaderClientPtr client) {
+  BindRequest(std::move(client), std::move(request));
   // Send the cached AppCacheResponse if any.
   if (info_.get())
     SendResponseInfo();
@@ -271,8 +275,8 @@ void AppCacheURLLoaderJob::OnResponseInfoLoaded(
     if (is_range_request())
       SetupRangeResponse();
 
-    if (IsResourceTypeFrame(request_.resource_type)) {
-      DCHECK(!main_resource_loader_callback_.is_null());
+    if (IsResourceTypeFrame(request_.resource_type) &&
+        main_resource_loader_callback_) {
       std::move(main_resource_loader_callback_)
           .Run(base::Bind(&AppCacheURLLoaderJob::Start, StaticAsWeakPtr(this)));
     }