Refactor how the updater state data is serialized in update checks.

components/update_client/configurator.h

 // Copyright 2014 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 COMPONENTS_UPDATE_CLIENT_CONFIGURATOR_H_
 #define COMPONENTS_UPDATE_CLIENT_CONFIGURATOR_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 114 matching lines @@
 
   // Returns a PrefService that the update_client can use to store persistent
   // update information. The PrefService must outlive the entire update_client,
   // and be safe to access from the thread the update_client is constructed
   // on.
   // Returning null is safe and will disable any functionality that requires
   // persistent storage.
   virtual PrefService* GetPrefService() const = 0;
 
   // Returns true if the Chrome is installed for the current user only, or false
-  // if Chrome is installed for all users on the machine.
+  // if Chrome is installed for all users on the machine. This function must be
+  // called only from a blocking pool thread, as it may access the file system.
   virtual bool IsPerUserInstall() const = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<Configurator>;
 
   virtual ~Configurator() {}
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_CONFIGURATOR_H_