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

net/http/http_auth_handler_mock.cc

Index: net/http/http_auth_handler_mock.cc
diff --git a/net/http/http_auth_handler_mock.cc b/net/http/http_auth_handler_mock.cc
index 9887937fef91017a2591c62131f1ce14cf0429f7..9331ae73da136e6dc690d89fc048a294988003ee 100644
--- a/net/http/http_auth_handler_mock.cc
+++ b/net/http/http_auth_handler_mock.cc
@@ -18,7 +18,9 @@ HttpAuthHandlerMock::HttpAuthHandlerMock()
     generate_async_(false), generate_rv_(OK),
     auth_token_(NULL),
     first_round_(true),
-    connection_based_(false) {
+    connection_based_(false),
+    allows_default_credentials_(false),
+    allows_explicit_credentials_(true) {
 }
 
 HttpAuthHandlerMock::~HttpAuthHandlerMock() {
@@ -73,7 +75,9 @@ void HttpAuthHandlerMock::SetGenerateExpectation(bool async, int rv) {
 
 HttpAuth::AuthorizationResult HttpAuthHandlerMock::HandleAnotherChallenge(
     HttpAuth::ChallengeTokenizer* challenge) {
-  if (!is_connection_based())
+  // If we receive an empty challenge for a connection based scheme, or a second
+  // challenge for a non connection based scheme, assume it's a rejection.
+  if (!is_connection_based() || challenge->base64_param().empty())
     return HttpAuth::AUTHORIZATION_RESULT_REJECT;
   if (!LowerCaseEqualsASCII(challenge->scheme(), "mock"))
     return HttpAuth::AUTHORIZATION_RESULT_INVALID;
@@ -84,6 +88,14 @@ bool HttpAuthHandlerMock::NeedsIdentity() {
   return first_round_;
 }
 
+bool HttpAuthHandlerMock::AllowsDefaultCredentials() {
+  return allows_default_credentials_;
+}
+
+bool HttpAuthHandlerMock::AllowsExplicitCredentials() {
+  return allows_explicit_credentials_;
+}
+
 bool HttpAuthHandlerMock::Init(HttpAuth::ChallengeTokenizer* challenge) {
   auth_scheme_ = HttpAuth::AUTH_SCHEME_MOCK;
   score_ = 1;