Don't try to use explicit credentials with schemes that don't support it.

net/http/http_auth_sspi_win.cc

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // See "SSPI Sample Application" at
 // http://msdn.microsoft.com/en-us/library/aa918273.aspx
 
 #include "net/http/http_auth_sspi_win.h"
 
 #include "base/base64.h"
 #include "base/logging.h"
@@ skipping 191 matching lines @@
   if (SecIsValidHandle(&cred_)) {
     library_->FreeCredentialsHandle(&cred_);
     SecInvalidateHandle(&cred_);
   }
 }
 
 bool HttpAuthSSPI::NeedsIdentity() const {
   return decoded_server_auth_token_.empty();
 }
 
+bool HttpAuthSSPI::AllowsExplicitCredentials() const {
+  return true;
+}
+
 void HttpAuthSSPI::Delegate() {
   can_delegate_ = true;
 }
 
 void HttpAuthSSPI::ResetSecurityContext() {
   if (SecIsValidHandle(&ctxt_)) {
     library_->DeleteSecurityContext(&ctxt_);
     SecInvalidateHandle(&ctxt_);
   }
 }
@@ skipping 198 matching lines @@
   int token_length = pkg_info->cbMaxToken;
   status = library->FreeContextBuffer(pkg_info);
   rv = MapFreeContextBufferStatusToError(status);
   if (rv != OK)
     return rv;
   *max_token_length = token_length;
   return OK;
 }
 
 }  // namespace net