ChromeOS: Add RenameCryptohome and migration code.

chromeos/cryptohome/homedir_methods.h

Index: chromeos/cryptohome/homedir_methods.h
diff --git a/chromeos/cryptohome/homedir_methods.h b/chromeos/cryptohome/homedir_methods.h
index 17f0f55a82101b75302a11bcf676687370e25de0..3f40f4a45afdc7283f282a3abffd7e3d6c150b5c 100644
--- a/chromeos/cryptohome/homedir_methods.h
+++ b/chromeos/cryptohome/homedir_methods.h
@@ -89,6 +89,12 @@ class CHROMEOS_EXPORT HomedirMethods {
                            const std::string& label,
                            const Callback& callback) = 0;
 
+  // Asks cryptohomed to change cryptohome identification |id_from| to |id_to|,
+  // which results in cryptohome directory renaming.
+  virtual void RenameCryptohome(const Identification& id_from,
+                                const Identification& id_to,
+                                const Callback& callback) = 0;
+
   // Creates the global HomedirMethods instance.
   static void Initialize();