getCollectionTime() does not count sub-ms pauses

We have seen intermittent failures with gc/cms/TestMBeanCMS.java. Error looks like this:

java.lang.RuntimeException: collectors found with zero time
at TestMBeanCMS.run(TestMBeanCMS.java:130)
at TestMBeanCMS.main(TestMBeanCMS.java:62)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:115)
at java.base/java.lang.Thread.run(Thread.java:834)