simpleperf: searching for debug files only when needed.

Currently simpleperf searches for debug files when creating Dso,
and may show a warning when a debug file has unmatched build id.
But not all debug files are needed. So this creates unnecessary
warnings.

This CL fixes it by searching for debug files only when needed.

Bug: 222563847
Test: run simpleperf_unit_test
Test: run pprof_proto_generator.py manually
Change-Id: Icc029af805e9cbdf5f53c36ae374b3b1d56dbc23
3 files changed