Add a "SystemProducer" layer which right now is just a dummy implementation.

This allows all platforms to have a empty implementation (which reduces
preprocessor macros), and later in this patch chain we will add a
implementation for android.

Bug: 966047
Change-Id: I5446f4da7f9de1e0cb4ecddf77a2142ad1868de6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624815
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662591}
9 files changed