[cpu-profiler] Add a HandleScope to limit memory consumption.

The handles created for each SharedFunctionInfo within
SourcePosition::InliningStack live for the life of the profile,
reaching 5MiB+ on an example server application for Node.

This HandleScope limits their lifetime locally, given that the handles
do not escape.

This saves ~10% of peak memory.

Bug: v8:7719
Change-Id: I97ce0fd3658be89fdd9cb9c1369ea5bfae0ce579
Reviewed-on: https://chromium-review.googlesource.com/1049647
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53085}