Expand comment for shouldUseCredentialStorage stub, explaining what it might...

webkit/glue/webframeloaderclient_impl.cc

Index: webkit/glue/webframeloaderclient_impl.cc
===================================================================
--- webkit/glue/webframeloaderclient_impl.cc	(revision 7352)
+++ webkit/glue/webframeloaderclient_impl.cc	(working copy)
@@ -211,12 +211,18 @@
 bool WebFrameLoaderClient::shouldUseCredentialStorage(DocumentLoader*,
     unsigned long identifier) {
   // FIXME
-  // Intended to call a method on the resource load delegate.
-  // Returns true for backward compatibility.
+  // Intended to pass through to a method on the resource load delegate.
+  // If implemented, that method controls whether the browser should ask the
+  // networking layer for a stored default credential for the page (say from
+  // the Mac OS keychain). If the method returns false, the user should be
+  // presented with an authentication challenge whether or not the networking
+  // layer has a credential stored.
+  // This returns true for backward compatibility: the ability to override the
+  // system credential store is new. (Actually, not yet fully implemented in
+  // WebKit, as of this writing.)
   return true;   
 }
 
-
 void WebFrameLoaderClient::dispatchDidReceiveAuthenticationChallenge(
     DocumentLoader*, unsigned long identifier, const AuthenticationChallenge&) {
   // FIXME