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

content/browser/loader/url_loader_request_handler.h

Index: content/browser/loader/url_loader_request_handler.h
diff --git a/content/browser/loader/url_loader_request_handler.h b/content/browser/loader/url_loader_request_handler.h
index fb0a1f4b2f31e521926888dc0f9ac9090e4e72a9..2bc22cac7ea67c0e484d5bb337516978acc3e748 100644
--- a/content/browser/loader/url_loader_request_handler.h
+++ b/content/browser/loader/url_loader_request_handler.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "content/public/common/url_loader.mojom.h"
 #include "content/public/common/url_loader_factory.mojom.h"
+#include "net/url_request/redirect_info.h"
 
 namespace content {
 
@@ -39,6 +40,26 @@ class CONTENT_EXPORT URLLoaderRequestHandler {
   // going forward. Subclasses who want to handle subresource requests etc may
   // want to override this to return a custom factory.
   virtual mojom::URLLoaderFactoryPtr MaybeCreateSubresourceFactory();
+
+  // Returns true if the handler delivers fallback content for the |response|
+  // passed. The |client| parameter points to the URLLoaderClient instance
+  // which is used for passing the fallback content and other information to
+  // the client. The |request| parameter points to the bound url request.
+  virtual bool MaybeGetFallbackForResponse(const ResourceResponseHead& response,
+                                           mojom::URLLoaderClientPtr* client,
+                                           mojom::URLLoaderRequest* request);
+
+  // Returns true if the handler delivers fallback content for the redirect
+  // |response| passed in. The |redirect_info| parameter contains the new
+  // location, etc. The |client| parameter points to the URLLoaderClient
+  // instance which is used for passing the fallback content and other
+  // information to the client. The |request| parameter points to the
+  // bound url request.
+  virtual bool MaybeGetFallbackForRedirect(
+      const ResourceResponseHead& response,
+      const net::RedirectInfo& redirect_info,
+      mojom::URLLoaderClientPtr* client,
+      mojom::URLLoaderRequest* request);
 };
 
 }  // namespace content