[Sync] Persist keystore key across restarts

sync/internal_api/sync_manager.h

Index: sync/internal_api/sync_manager.h
diff --git a/sync/internal_api/sync_manager.h b/sync/internal_api/sync_manager.h
index 83b8ccbc57e587fd31883bf29830d4691a04da06..a28c41d9223c118b81622641bbab505f581fdae4 100644
--- a/sync/internal_api/sync_manager.h
+++ b/sync/internal_api/sync_manager.h
@@ -459,6 +459,7 @@ class SyncManager {
             const SyncCredentials& credentials,
             sync_notifier::SyncNotifier* sync_notifier,
             const std::string& restored_key_for_bootstrapping,
+            const std::string& restored_keystore_key_for_bootstrapping,
             bool keystore_encryption_enabled,
             TestingMode testing_mode,
             browser_sync::Encryptor* encryptor,
@@ -536,6 +537,10 @@ class SyncManager {
   // May be called on any thread.
   bool IsUsingExplicitPassphrase();
 
+  // Extracts the keystore encryption bootstrap token if a keystore key existed.
+  // Returns true if bootstrap token successfully extracted, false otherwise.
+  bool GetKeystoreKeyBootstrapToken(std::string* token);
+
   // Call periodically from a database-safe thread to persist recent changes
   // to the syncapi model.
   void SaveChanges();