Metrics provider for statistical stack profiler

Provides a metrics provider that uploads statistical stack profiling
state via UMA.

This CL builds on top of the statistical profiler implementation in
https://crrev.com/1016563004, which is under review.

BUG=464929

Review URL: https://codereview.chromium.org/981143006

Cr-Commit-Position: refs/heads/master@{#321928}
12 files changed