I am the one who originally added this sleep call to WebKit, when we first imported TCMalloc to use as our custom allocator. It was indeed there for a reason, but that reason is not applicable to WebKit's allocation patterns. TCMalloc was designed for a server workload, over time we have adapted it more to the unique needs of a browser engine. This change may help other operations, but probably not as much as the GC benchmark in question.