[Sync] Implement keystore migration support.

sync/engine/conflict_resolver.cc

Index: sync/engine/conflict_resolver.cc
diff --git a/sync/engine/conflict_resolver.cc b/sync/engine/conflict_resolver.cc
index 736e6682b213887cf717b1c5ecfeb346b1483fdc..0dfb0c34c75e6d612d81794d8999411b280adabc 100644
--- a/sync/engine/conflict_resolver.cc
+++ b/sync/engine/conflict_resolver.cc
@@ -257,10 +257,10 @@ ConflictResolver::ProcessSimpleConflict(WriteTransaction* trans,
       // reset that passphrase as an explicit one via settings. The goal here
       // is to ensure both sets of encryption keys are preserved.
       if (cryptographer->is_ready()) {
-        cryptographer->GetKeys(server_nigori->mutable_encrypted());
-        server_nigori->set_using_explicit_passphrase(
-            entry.Get(syncable::SPECIFICS).nigori().
-                using_explicit_passphrase());
+        cryptographer->GetKeys(server_nigori->mutable_encryption_keybag());
+        server_nigori->set_frozen_keybag(
+            entry.Get(syncable::SPECIFICS).nigori().frozen_keybag());
+        // TODO(zea): tackle migration-induced conflicts here.
       }
       // We deliberately leave the server's device information. This client will
       // add its own device information on restart.