r206189 "Add new logging for network resource loading" added a new error in WebLoaderStrategy::loadResource:
RELEASE_LOG_ERROR_IF_ALLOWED(frame, "loadResource: Unable to create SubresourceLoader (frame = %p", &frame);
However, this error statement is hit during normal operation when there is no error, whenever a load is canceled by changing the URL of an API::URLRequest to NULL during a willSendRequestForFrame callback (see InjectedBundlePageResourceLoadClient::willSendRequestForFrame). For example, the error statement is printed once each time Epiphany's adblocker blocks an ad.
Either (a) WebLoaderStrategy::loadResource should never be called when the load has already been canceled, or (b) WebLoaderStrategy::loadResource should not print an error in this case. Not sure which way is correct, but I don't plan to investigate (a) so here is a patch to do (b).
Created attachment 291489 [details]
Makes sense to me. Looking deeper, I can see that there are many checks in the creation of a SubresourceLoader that could cause it to return false/null.
Adding Antti, who reviewed the original patch.
Comment on attachment 291489 [details]
Clearing flags on attachment: 291489
Committed r207414: <http://trac.webkit.org/changeset/207414>
All reviewed patches have been landed. Closing bug.