This change adds platform-dependent services that handle creating
semaphores and importing image memory. Then, we use them to wrap a
texture from an outside source, and release a signal semaphore back
when we're done with it. This will be used to allow chrome to render
dawn on Vulkan platforms.
Bug: chromium:976495
Change-Id: I9f07eaf436e10aa6bd88cffdc74fd23834d62ee0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/8340
Commit-Queue: Idan Raiter <idanr@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
