simpleperf: add inplace-sampler event type.

Add inplace-sampler event type, so it can be used in
record/list command. This cl doesn't add code for communicating
with profiled process, and fake records in InplaceSamplerClient.cpp
for testing purpose.
Refactor runtest.py to test inplace-sampler profiling.

Bug: http://b/30974760
Test: run runtest.py --inplace-sampler.
Change-Id: I92d8b03583c58b3589207f5c655e03853899be3a
24 files changed