Return times in future in peekWhenForTest.

Previously peekWhenForTest only returns a value if when <= current time.
This contradicts the spec for TestLooperManager#peekWhen.

Flag: android.os.message_queue_testability
Bug: 112000181
Test: atest TestLooperManagerTest
Change-Id: Ic3dcb2b9c0230786ca33245debae2bb4b549abc1