Add google_update::GetUntrustedDataValueFromTag()

chrome/installer/util/google_update_util.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_UTIL_GOOGLE_UPDATE_UTIL_H_
 #define CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_UTIL_H_
 
 #include <string>
 
 namespace google_update {
 
 // If user-level Google Update is absent, calls the system-level
 // GoogleUpdateSetup.exe to install it, and waits until it finishes.
 // Returns true if already installed, installed successfully, or
 // if Google Update is not present at system-level.
 // Returns false if the installation fails.
 bool EnsureUserLevelGoogleUpdatePresent();
 
 // Tell Google Update that an uninstall has taken place.  This gives it a chance
 // to uninstall itself straight away if no more products are installed on the
 // system rather than waiting for the next time the scheduled task runs.
 // Returns false if Google Update could not be executed, or times out.
 bool UninstallGoogleUpdate(bool system_install);
 
 // Returns the value corresponding to |key| in untrusted data passed from
 // Google Update.  Returns an empty string if |key| is absent or if its value
 // contains non-printable characters.
 std::string GetUntrustedDataValue(const std::string& key);
 
+// Returns the value corresponding to |key| in untrusted data passed from
+// |tag|.  Returns an empty string if |key| is absent or if its value

[grt (UTC plus 2), 2014/03/03 15:18:26]

please document the expected format of |tag|.

[jackhou1, 2014/03/04 00:56:28]

Done.

+// contains non-printable characters.
+std::string GetUntrustedDataValueFromTag(const std::string& tag,
+                                         const std::string& key);
+
 }  // namespace google_update
 
 #endif  // CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_UTIL_H_