simpleperf: support hotplug events in record cmd.
1. When a cpu is down, read records from event files on that cpu,
then close those event files.
2. When a cpu is up, open event files on that cpu, and create
mapped buffer for those event files to dump records.
3. Instead of creating a mapped buffer for each event type on each
cpu, we can just create a mapped buffer for all event types on
each cpu.
4. When new event files are created, store a EventIdRecord record in
perf.data to notify record_file_reader.cpp.
Bug: http://b/29245608
Test: run simpleperf record cmd and make cpu offline and online.
Test: run simpleperf_unit_test.
Change-Id: Ib97a24b6292fa143e9b35cb105bdddf1e826d60a
12 files changed