Make ResourceFetcher return Resources with LoadError instead of nullptrs.

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 172 matching lines @@
     case Resource::ImportResource:
       resource = RawResource::fetchImport(request, fetcher());
       break;
     case Resource::Raw:
       resource = RawResource::fetch(request, fetcher());
       break;
     default:
       NOTREACHED();
   }
 
-  if (resource)
+  // CSP layout tests verify that preloads are subject to access checks by
+  // seeing if they are in the `preload started` list. Therefore do not add
+  // them to the list if the load is immediately denied.
+  if (resource && !resource->resourceError().isAccessCheck())
     fetcher()->preloadStarted(resource);
   return resource;
 }
 
 void DocumentLoader::didRedirect(const KURL& oldURL, const KURL& newURL) {
   timing().addRedirect(oldURL, newURL);
 
   // If a redirection happens during a back/forward navigation, don't restore
   // any state from the old HistoryItem. There is a provisional history item for
   // back/forward navigation only. In the other case, clearing it is a no-op.
@@ skipping 470 matching lines @@
   }
 
   DEFINE_STATIC_LOCAL(
       ResourceLoaderOptions, mainResourceLoadOptions,
       (DoNotBufferData, AllowStoredCredentials, ClientRequestedCredentials,
        CheckContentSecurityPolicy, DocumentContext));
   FetchRequest fetchRequest(m_request, FetchInitiatorTypeNames::document,
                             mainResourceLoadOptions);
   m_mainResource =
       RawResource::fetchMainResource(fetchRequest, fetcher(), m_substituteData);
-  if (!m_mainResource) {
+
+  // PlzNavigate:
+  // The final access checks are still performed here, potentially rejecting
+  // the "provisional" load, but the browser side already expects the renderer
+  // to be able to unconditionally commit.
+  if (!m_mainResource || (m_frame->settings()->browserSideNavigationEnabled() &&
+                          m_mainResource->errorOccurred())) {
     m_request = ResourceRequest(blankURL());
     maybeLoadEmpty();
     return;
   }
   // A bunch of headers are set when the underlying resource load begins, and
   // m_request needs to include those. Even when using a cached resource, we may
   // make some modification to the request, e.g. adding the referer header.
   m_request = m_mainResource->isLoading() ? m_mainResource->resourceRequest()
                                           : fetchRequest.resourceRequest();
   m_mainResource->addClient(this);
@@ skipping 57 matching lines @@
                              m_writer ? m_writer->encoding() : emptyAtom, true,
                              ForceSynchronousParsing);
   if (!source.isNull())
     m_writer->appendReplacingData(source);
   endWriting(m_writer.get());
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 }  // namespace blink