Add Timestamp column to refs table

Change-Id: I6a6ca62527108998968b3a7b7e563fd9c1d9db78

src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/DatabaseSchemaCreator.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/DatabaseSchemaCreator.java b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/DatabaseSchemaCreator.java
index 2990a1b..0bf042e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/DatabaseSchemaCreator.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/DatabaseSchemaCreator.java
@@ -60,7 +60,9 @@
                       + "token TIMESTAMP OPTIONS (allow_commit_timestamp = true),"
                       + "owner STRING(MAX) NOT NULL"
                       + ")"
-                      + "PRIMARY KEY (project, ref)"),
+                      + "PRIMARY KEY (project, ref)",
+                  "ALTER TABLE refs ADD COLUMN IF NOT EXISTS "
+                      + "time TIMESTAMP OPTIONS (allow_commit_timestamp=true)"),
               null)
           .get();
     } catch (Exception e) {

src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/SpannerRefDatabase.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/SpannerRefDatabase.java b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/SpannerRefDatabase.java
index d291831..e8ad5b2 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/SpannerRefDatabase.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/SpannerRefDatabase.java
@@ -25,6 +25,7 @@
 import com.google.cloud.spanner.ResultSet;
 import com.google.cloud.spanner.Statement;
 import com.google.cloud.spanner.Struct;
+import com.google.cloud.spanner.Value;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.entities.Project;
@@ -133,6 +134,8 @@
               if (row == null || row.getString(0).equals(expectedValue)) {
                 transaction.buffer(
                     Mutation.newInsertOrUpdateBuilder("refs")
+                        .set("time")
+                        .to(Value.COMMIT_TIMESTAMP)
                         .set("project")
                         .to(project.get())
                         .set("ref")