Add interval for relayout perf test

So if there are messages posted to other threads in relayout, they
won't affect the next round to execute relayout. And the continuous
invocation isn't common in the real case.

Bug: 129527548
Test: atest RelayoutPerfTest
Change-Id: I0081fc7a80271ee3dd97c19a6ae7e3bc13ae8a8b