Migrate Libsecret for OSCrypt to a new schema

components/os_crypt/key_storage_libsecret.h

Index: components/os_crypt/key_storage_libsecret.h
diff --git a/components/os_crypt/key_storage_libsecret.h b/components/os_crypt/key_storage_libsecret.h
index 2560b5440bbdb2c3a23394a58583b0bdd4d7fbc4..18f7ad34de6f1d0c69661c5815947fa7dedbdcde 100644
--- a/components/os_crypt/key_storage_libsecret.h
+++ b/components/os_crypt/key_storage_libsecret.h
@@ -26,6 +26,12 @@ class KeyStorageLibsecret : public KeyStorageLinux {
  private:
   std::string AddRandomPasswordInLibsecret();
 
+  // TODO(crbug.com/639298) Older Chromium releases stored passwords with a
+  // problematic schema. Detect password entries with the old schema and migrate
+  // them to the new schema. Returns the migrated password or an empty string if
+  // none we migrated.
+  std::string Migrate();
+
   DISALLOW_COPY_AND_ASSIGN(KeyStorageLibsecret);
 };