[net/auth] Move MockAuthLibrary declaration to platform files.

This mildly reduces the number of platform specific code in files that
are supposed to be cross platform.

R=eroman@chromium.org

Bug: 927182
Change-Id: I854f452ac95a9dbeca326821d7efd9c2ea4c61b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1693565
Commit-Queue: Asanka Herath <asanka@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680094}

net/android/dummy_spnego_authenticator.h

@@ -137,6 +137,9 @@ class DummySpnegoAuthenticator {
 };
 
 }  // namespace android
+
+using MockAuthLibrary = android::DummySpnegoAuthenticator;
+
 }  // namespace net
 
 #endif  // NET_ANDROID_DUMMY_SPNEGO_AUTHENTICATOR_H_

net/http/http_auth_handler_negotiate_unittest.cc

@@ -36,6 +36,8 @@
 #include "net/http/mock_sspi_library_win.h"
 #elif BUILDFLAG(USE_EXTERNAL_GSSAPI)
 #include "net/http/mock_gssapi_library_posix.h"
+#else
+#error "use_kerberos is true, but no Kerberos implementation available."
 #endif
 
 using net::test::IsError;
@@ -45,16 +47,6 @@ namespace net {
 
 constexpr char kFakeToken[] = "FakeToken";
 
-#if defined(OS_ANDROID)
-using MockAuthLibrary = net::android::DummySpnegoAuthenticator;
-#elif defined(OS_WIN)
-using MockAuthLibrary = MockSSPILibrary;
-#elif BUILDFLAG(USE_EXTERNAL_GSSAPI)
-using MockAuthLibrary = test::MockGSSAPILibrary;
-#else
-#error "use_kerberos is true, but no Kerberos implementation available."
-#endif
-
 class HttpAuthHandlerNegotiateTest : public PlatformTest,
                                      public WithScopedTaskEnvironment {
  public:

net/http/mock_gssapi_library_posix.h

@@ -203,6 +203,8 @@ class MockGSSAPILibrary : public GSSAPILibrary {
 
 }  // namespace test
 
+using MockAuthLibrary = test::MockGSSAPILibrary;
+
 }  // namespace net
 
 #endif  // NET_HTTP_MOCK_GSSAPI_LIBRARY_POSIX_H_

net/http/mock_sspi_library_win.h

@@ -106,6 +106,8 @@ class MockSSPILibrary : public SSPILibrary {
   std::set<PSecPkgInfoW> expected_freed_packages_;
 };
 
+using MockAuthLibrary = MockSSPILibrary;
+
 }  // namespace net
 
 #endif  // NET_HTTP_MOCK_SSPI_LIBRARY_WIN_H_