simpleperf: refactor code setting sample rate
To allow setting different sample rates for different
events, EventSelectionSet returns group id when adding
new events and allows setting sample rate for a group
id. But this makes user code more complex. Because it
needs to remeber group ids and set sample rate for each
group id.
To simplify this, let EventSelectionSet remember the
current sample rate, and use it when adding new events.
So the user code only needs to add new events and set
new sample rates.
Also rename SampleSpeed to SampleRate.
Bug: 304600718
Test: run simpleperf_unit_test
Change-Id: I24770945f3c315d1d4d73ed837160f5975b1ce91
7 files changed