Add webgpu-headers to fetch_dawn_dependencies.py

Dawn build now requires webgpu.json from webgpu-headers, so add it to
fetch_dawn_dependencies for non-gclient based build setups.

Hopefully fixes Dawn->Skia roll which uses DAWN_FETCH_DEPENDENCIES.

Fixed: 452983507
Bug: 434977307
Change-Id: If201ce863ed9dc9861edd78ed9db1b62e4f7c1b2
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/267574
Auto-Submit: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
diff --git a/tools/fetch_dawn_dependencies.py b/tools/fetch_dawn_dependencies.py
index 2296885..151a26c 100644
--- a/tools/fetch_dawn_dependencies.py
+++ b/tools/fetch_dawn_dependencies.py
@@ -114,6 +114,7 @@
         'third_party/vulkan-headers/src',
         'third_party/vulkan-loader/src',
         'third_party/vulkan-utility-libraries/src',
+        'third_party/webgpu-headers/src',
     ]
 
     root_dir = Path(args.directory).resolve()