GCAPI should append to the existing experiment_labels instead of clobbering them.

chrome/installer/util/google_update_constants.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.
 
 // Defines all the command-line switches used with Google Update.
 
 #ifndef CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_CONSTANTS_H_
 #define CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_CONSTANTS_H_
 
 namespace google_update {
 
 // The GUID Google Update uses to keep track of Chrome upgrades.
 extern const wchar_t kChromeUpgradeCode[];
 
 // The name of the value where Google Update reads the list of experiments for
 // itself and Chrome.
 extern const wchar_t kExperimentLabels[];
 
+// The separator used to separate items in kExperimentLabels.
+extern const wchar_t kExperimentLabelSep[];
+
 // The GUID Google Update uses to keep track of Google Update self-upgrades.
 extern const wchar_t kGoogleUpdateUpgradeCode[];
 
 extern const wchar_t kGoogleUpdateSetupExe[];
 
 extern const wchar_t kRegPathClients[];
 
 // The difference between ClientState and ClientStateMedium is that the former
 // lives on HKCU or HKLM and the later always lives in HKLM. ClientStateMedium
 // is primarily used for consent of the EULA and stats collection. See bug
@@ skipping 45 matching lines @@
 extern const wchar_t kRegUsageStatsField[];
 extern const wchar_t kRegVersionField[];
 extern const wchar_t kRegWebAccessibleField[];
 
 // last time that chrome ran in the Time internal format.
 extern const wchar_t kRegLastRunTimeField[];
 
 }  // namespace google_update
 
 #endif  // CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_CONSTANTS_H_