Fixing concurrency bug in CloseGuardTester.

Hudson was complaining with this exception:
java.util.ConcurrentModificationException
	at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:576)
	at libcore.dalvik.system.CloseGuardTester.assertEverythingWasClosed(CloseGuardTester.java:59)
	at libcore.java.lang.ProcessBuilderTest.testDestroyDoesNotLeak(ProcessBuilderTest.java:91)

Change-Id: Ie6be12186c94e14ba4d5df8a392144269abb598b
1 file changed