GitLab

This metric records frames sent by AVDA, bucketed by whether they
are or are not overlays.

The goal is to provide an approximate count of how often SurfaceView
is used versus SurfaceTexture.

BUG=629313

Review-Url: https://codereview.chromium.org/2163513002
Cr-Commit-Position: refs/heads/master@{#406712}