Remove 'using base::string16;' from base/strings/string16.h and remove temporary

chrome/browser/autocomplete/history_url_provider_unittest.cc

 // Copyright (c) 2012 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 "chrome/browser/autocomplete/history_url_provider.h"
 
 #include <algorithm>
 
 #include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
@@ skipping 988 matching lines @@
       output[max_matches].url = URLFixerUpper::FixupURL(
           test_cases[i].matches[max_matches].url, std::string()).spec();
       output[max_matches].allowed_to_be_default_match = true;
     }
     autocomplete_->scoring_params_ = test_cases[i].scoring_params;
 
     // Test the control (scoring disabled).
     autocomplete_->scoring_params_.experimental_scoring_enabled = false;
     ASSERT_NO_FATAL_FAILURE(
         RunTest(ASCIIToUTF16(test_cases[i].input),
-                string16(), false, output, max_matches));
+                base::string16(), false, output, max_matches));
     for (int j = 0; j < max_matches; ++j) {
       EXPECT_EQ(test_cases[i].matches[j].control_relevance,
                 matches_[j].relevance);
     }
 
     // Test the experiment (scoring enabled).
     autocomplete_->scoring_params_.experimental_scoring_enabled = true;
     ASSERT_NO_FATAL_FAILURE(
         RunTest(ASCIIToUTF16(test_cases[i].input),
-                string16(), false, output, max_matches));
+                base::string16(), false, output, max_matches));
     for (int j = 0; j < max_matches; ++j) {
       EXPECT_EQ(test_cases[i].matches[j].experiment_relevance,
                 matches_[j].relevance);
     }
   }
 }