[Fuchsia] Enable ExternalVkImageBacking on Fuchsia

Now ExternalVkImageBacking compiles and can be used on Fuchsia. GL
integration is not implemented yet (which depends on ANGLE integration).

Bug: 766360, 934526
Change-Id: I61c8e9a3790f5bb1f5197b8ed9bde59f1dc2069c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1542617
Commit-Queue: Sergey Ulanov <[email protected]>
Reviewed-by: Antoine Labour <[email protected]>
Reviewed-by: Michael Spang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#647858}
16 files changed