Zero-init Dawn structs

Needed for https://dawn-review.googlesource.com/c/dawn/+/24622
and https://dawn-review.googlesource.com/c/dawn/+/24620

Bug: none, dawn:22
Change-Id: I22e6dd8d695060f01e29d9c9c51e03233c0a6ef7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2292833
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#787462}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 7c71626bdc4358c8ce07ea54c3d0672e8e78a509
4 files changed