This is a reland of 7bb6cd63
Original change's description:
> [coverage] Ship block coverage
> 
> Enables block coverage by default.
> 
> Design doc: http://goo.gl/hSJhXn
> Tracking bug: http://crbug.com/v8/6000
> 
> Bug: v8:6000
> Change-Id: I8c56474473b60e4707b75dc601b3e88455861a27
> Reviewed-on: https://chromium-review.googlesource.com/583093
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46898}

Bug: v8:6000
Change-Id: I033d89a35c23fcff083f83103df45e33f7962d67
Reviewed-on: https://chromium-review.googlesource.com/592968
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47003}