base: Remove using declaration from test_suite.h header.

sandbox/win/tests/unit_tests/unit_tests.cc

 // 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.
 
 #include "base/bind.h"
 #include "base/test/launcher/unit_test_launcher.h"
 #include "base/test/test_suite.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 int wmain(int argc, wchar_t **argv) {
   if (argc >= 2) {
     if (0 == _wcsicmp(argv[1], L"-child"))
       // This instance is a child, not the test.
       return 0;
   }
 
-  TestSuite test_suite(argc, argv);
+  base::TestSuite test_suite(argc, argv);
   return base::LaunchUnitTests(
       argc,
       argv,
       false,
       base::Bind(&base::TestSuite::Run, base::Unretained(&test_suite)));
 }