Add base:: to string16s in chrome/.

chrome/installer/gcapi/gcapi_omaha_experiment.h

 // 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.
 
 #ifndef CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_
 #define CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_
 
 #include "base/strings/string16.h"
 
 namespace gcapi_internals {
 
 extern const wchar_t kReactivationLabel[];
 extern const wchar_t kRelaunchLabel[];
 
 // Returns the full experiment label to be used by |label| (which is one of the
 // labels declared above) for |brand_code|.
-string16 GetGCAPIExperimentLabel(const wchar_t* brand_code,
-                                 const string16& label);
+base::string16 GetGCAPIExperimentLabel(const wchar_t* brand_code,
+                                       const base::string16& label);
 
 }  // namespace gcapi_internals
 
 // Writes a reactivation brand code experiment label in the Chrome product and
 // binaries registry keys for |brand_code|. This experiment label will have a
 // expiration date of now plus one year. If |shell_mode| is set to
 // GCAPI_INVOKED_UAC_ELEVATION, the value will be written to HKLM, otherwise
 // HKCU. A user cannot have both a reactivation label and a relaunch label set
 // at the same time (they are mutually exclusive).
 bool SetReactivationExperimentLabels(const wchar_t* brand_code, int shell_mode);
 
 // Writes a relaunch brand code experiment label in the Chrome product and
 // binaries registry keys for |brand_code|. This experiment label will have a
 // expiration date of now plus one year. If |shell_mode| is set to
 // GCAPI_INVOKED_UAC_ELEVATION, the value will be written to HKLM, otherwise
 // HKCU. A user cannot have both a reactivation label and a relaunch label set
 // at the same time (they are mutually exclusive).
 bool SetRelaunchExperimentLabels(const wchar_t* brand_code, int shell_mode);
 
 #endif  // CHROME_INSTALLER_GCAPI_GCAPI_OMAHA_EXPERIMENT_H_