This helps output in the headers information about which structure can
be used to extend which. In the future it could also be used to generate
helpers that validate that the chain for a root structure contains only
allowed extension structs.
Fixed: dawn:1486
Change-Id: I6134332d477503e242b3bec9f8e9bedeeb352351
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/96000
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>