Newer perf.data contains both MMAP and MMAP2 record type,
but MMAP2 record type is not supported in previous ll_prof,
MMAP2 record information will be lost.

BUG=v8:4569
LOG=n

Review URL: https://codereview.chromium.org/1469153004

Cr-Commit-Position: refs/heads/master@{#32319}