Update dependencies in python fetch script

Also do not error on missing deps variable

Change-Id: I987b6ada21f28061fe5cee3bcc4eb91ac5ab8a54
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/191622
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/tools/fetch_dawn_dependencies.py b/tools/fetch_dawn_dependencies.py
index 4c80f9c..3c6d29a 100644
--- a/tools/fetch_dawn_dependencies.py
+++ b/tools/fetch_dawn_dependencies.py
@@ -101,6 +101,8 @@
         'third_party/jinja2',
         'third_party/khronos/EGL-Registry',
         'third_party/khronos/OpenGL-Registry',
+        'third_party/libprotobuf-mutator/src',
+        'third_party/protobuf',
         'third_party/markupsafe',
         'third_party/glslang/src',
         'third_party/spirv-headers/src',
@@ -140,9 +142,9 @@
     variables = ldict.get('vars', {})
 
     if deps is None:
-        log(f"ERROR: DEPS file '{deps_path}' does not define a 'deps' variable"
+        log(f"WARNING: DEPS file '{deps_path}' does not define a 'deps' variable"
             )
-        exit(1)
+        return
 
     for submodule in required_submodules:
         if submodule not in deps: