Vendored Guava should not use reflection

src/main/java/org/jenkinsci/plugins/workflow/support/concurrent/ChainingListenableFuture.java

@@ -3,7 +3,6 @@
 import com.google.common.util.concurrent.AbstractFuture;
 import com.google.common.util.concurrent.AsyncFunction;
 import com.google.common.util.concurrent.ListenableFuture;
-import com.google.common.util.concurrent.MoreExecutors;
 
 import javax.annotation.Nullable;
 import java.lang.reflect.UndeclaredThrowableException;
@@ -30,6 +29,7 @@
  * in a {@code UndeclaredThrowableException} so that this class can get
  * access to the cause.
  */
+@Deprecated
 class ChainingListenableFuture<I, O>
     extends AbstractFuture<O> implements Runnable {
 
@@ -208,7 +208,7 @@ public void run() {
               ChainingListenableFuture.this.outputFuture = null;
             }
           }
-        }, Futures.newExecutorService());
+        }, MoreExecutors.directExecutor());
     } catch (UndeclaredThrowableException e) {
       // Set the cause of the exception as this future's exception
       setException(e.getCause());

src/main/java/org/jenkinsci/plugins/workflow/support/concurrent/DirectExecutor.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2007 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package org.jenkinsci.plugins.workflow.support.concurrent;
+
+import com.google.common.annotations.GwtCompatible;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+import java.util.concurrent.Executor;
+
+/**
+ * An {@link Executor} that runs each task in the thread that invokes {@link Executor#execute
+ * execute}.
+ */
+@GwtCompatible
+@Restricted(NoExternalUse.class)
+enum DirectExecutor implements Executor {
+  INSTANCE;
+
+  @Override
+  public void execute(Runnable command) {
+    command.run();
+  }
+
+  @Override
+  public String toString() {
+    return "MoreExecutors.directExecutor()";
+  }
+}