Reviewed by Adele

    Reviewed by Adele

        <rdar://problem/5525770> REGRESSION: HTTP Auth protected favicon request results in a password sheet

        Some http-auth protected sites have the main resource(s) unprotected, but many subresources are
        protected by authentication.  Occasionally one can view the main page of a site but the favicon
        is behind the iron curtain - in these cases, we should *not* prompt for a username and password
        solely for the favicon.

        * loader/ResourceLoader.h: Make didReceiveAuthenticationChallenge virtual

        * loader/SubresourceLoader.cpp:
        (WebCore::SubresourceLoader::didReceiveAuthenticationChallenge): Now that this method
          is virtual from ResourceLoader, SubresourceLoader can override.  First call to the
          SubresourceLoaderClient.  If they cancel the resource load, return early. Otherwise, let
          ResourceLoader work its magic (resulting in the auth sheet coming down)
        * loader/SubresourceLoader.h:

        * loader/SubresourceLoaderClient.h:
        (WebCore::SubresourceLoaderClient::didReceiveAuthenticationChallenge):

        * loader/icon/IconLoader.cpp:
        (WebCore::IconLoader::didReceiveAuthenticationChallenge): Cancel the resource load, since we should
          never prompt the user for credentials just for a favicon.
        * loader/icon/IconLoader.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@28830 268f45cc-cd09-0410-ab3c-d52691b4dbfc