Simpleperf: do stack unwinding while recording.

Dumping user's stack consumes lots of disk space, which makes long period recording
impossible. This patch does stack unwinding before writing to perf.data, so it doesn't
need to save user's stack. Previous behavior is still supported with --post-unwind option.

A record cache is used for online record processing.

Bug: 22229391
Change-Id: Idcc6ec46924fff3fcc8c165d62f8af875b173cd4
8 files changed