Always pass an Executor to Futures methods

Among the Futures methods that run user callbacks, those that don't take
an Executor will be deleted. This change migrates them to the
counterparts that take MoreExecutors.directExecutor() as such Executor
in the parameter list, exactly the way that the old method works.

PiperOrigin-RevId: 148985066
Change-Id: I38bb9f442cbbc795b2c66a023850d0d35d255aeb

gerrit-lucene/src/main/java/com/google/gerrit/lucene/AbstractLuceneIndex.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.lucene;
 
+import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 
 import com.google.common.base.Joiner;
@@ -288,7 +289,8 @@ public abstract class AbstractLuceneIndex<K, V> implements Index<K, V> {
             reopenThread.waitForGeneration(gen, 0);
             return new NrtFuture(gen);
           }
-        });
+        },
+        directExecutor());
   }
 
   @Override