Add test to ensure that URLs that redirect inside the PDF plugin fail to load

pdf/document_loader.h

Index: pdf/document_loader.h
diff --git a/pdf/document_loader.h b/pdf/document_loader.h
index cf85e99e5a1add35f6ef865815f2581805f31a28..583055ad8af05e5c1096e2a09468fdbfdc191b02 100644
--- a/pdf/document_loader.h
+++ b/pdf/document_loader.h
@@ -39,6 +39,8 @@ class DocumentLoader {
     virtual void OnNewDataAvailable() = 0;
     // Notification called when document is fully loaded.
     virtual void OnDocumentComplete() = 0;
+    // Notification called if the document unrecoverably fails to load.
+    virtual void DocumentLoadFailed() = 0;
   };
 
   explicit DocumentLoader(Client* client);