Chromium builds the Vulkan loader without support Xlib (because it
prefers XCB) which caused Xlib wgpu::SwapChain creation to fail on the
Vulkan backend.
This CL adds a fallback to use VK_KHR_xcb_surface if VK_KHR_xlib_surface
isn't present.
Bug: dawn:662
Change-Id: I0e0128ee6b5c75da03998dbae231d17e48bacc81
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/41180
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>