DEPS: Only add vulkan-deps in dawn_standalone.

This avoids adding a duplicate of vulkan-deps when Chromium
recursedeps into Dawn that recursedeps into vulkan-deps.

Bug: tint:700

Change-Id: I0f1797e0850f4cb4ab1ba16e641d859e8e376994
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/46740
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
diff --git a/DEPS b/DEPS
index 5d46831..b294242 100644
--- a/DEPS
+++ b/DEPS
@@ -128,6 +128,7 @@
 
   'third_party/vulkan-deps': {
     'url': '{chromium_git}/vulkan-deps@105af117f0532953577198cc9bd8ee6f76c29009',
+    'condition': 'dawn_standalone',
   },
 
   'third_party/zlib': {