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.
393216 is the number of bytes for peek memory.
262144 is the number of bytes for current memory.

Not too much, but a good proof of concept.