add a test case indicating we reset the stats when starting a new fragme...

...nt

Don't merge. Also bypass the bug of ENG-6517 by using inequality checking instead of equality checking.

Still need to discuss on the test case which indicates the peak memory usage is larger than the "current" memory usage.
If you use a different set of variables to cache the deleteProc etc., you can simplify the test by not repeating the initialization of selectBottomFrag, saving many lines of code below.