The approximate mode enables taking an approximate stack trace from GC,
where the top frames might be missing if inlined. Note that in that case,
the frame summary will refer to optimized code, so it will not be possible
to take source position. (The user of the summary will have to handle the
case frame_summary.abstract_code()->kind() == AbstractCode::OPTIMIZED_CODE
specially.)

Review URL: https://codereview.chromium.org/1907443002

Cr-Commit-Position: refs/heads/master@{#35728}