LazySingletonAspectInstanceFactoryDecorator uses shared singleton mutex

Issue: SPR-14241

spring-aop/src/test/java/org/springframework/aop/aspectj/annotation/AbstractAspectJAdvisorFactoryTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -693,6 +693,11 @@ public abstract class AbstractAspectJAdvisorFactoryTests {
 			return new AspectMetadata(PerTypeWithinAspect.class, "perTypeWithin");
 		}
 
+		@Override
+		public Object getAspectCreationMutex() {
+			return this;
+		}
+
 		@Override
 		public int getOrder() {
 			return Ordered.LOWEST_PRECEDENCE;