Try to use the vulkan-headers from vulkan-deps instead of third_party/khronos.

Change-Id: Ic4af5ec86e4ea2ec404a6e32e49068fc5993d55a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/85300
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Loko Kung <lokokung@google.com>

scripts/dawn_overrides_with_defaults.gni

@@ -54,6 +54,14 @@ if (!defined(dawn_swiftshader_dir)) {
   dawn_swiftshader_dir = ""
 }
 
+if (!defined(dawn_vulkan_headers_dir)) {
+  dawn_vulkan_headers_dir = "//third_party/vulkan-deps/vulkan-headers/src"
+  if (dawn_standalone) {
+    dawn_vulkan_headers_dir =
+        "${dawn_root}/third_party/vulkan-deps/vulkan-headers/src"
+  }
+}
+
 if (!defined(dawn_vulkan_loader_dir)) {
   # Default to the Vulkan loader not being available except in standalone.
   dawn_vulkan_loader_dir = ""