GitLab

Make Poisson sampler a separate class that is responsible for listening
for allocation and doing the sampling with given sampling interval.

SamplingHeapProfiler is now an observer of PoissonAllocationObserver.
Once a sample added it record the native stack and stores the sample
in the map. The list of recorded samples can then be retrieved by clients.

TBR=ajwong@chromium.org
BUG=803276

Change-Id: I1e568b9839d9cc0099704ba1b9f047c14a46a0ee
Reviewed-on: https://chromium-review.googlesource.com/1189713Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586369}