Fix RPDesc::occlusionQuerySet not defaulting to nullptr

The default value for optional object structure members wasn't set
correctly for C++ structures.

Bug: dawn:22
Change-Id: I09e7f3675f6e0b5990ddcf03601b3b91cd25f553
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/31200
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Shaobo Yan <shaobo.yan@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

dawn.json

@@ -644,7 +644,7 @@
                 "name": "create swap chain",
                 "returns": "swap chain",
                 "args": [
-                    {"name": "surface", "type": "surface", "optional": "true"},
+                    {"name": "surface", "type": "surface"},
                     {"name": "descriptor", "type": "swap chain descriptor", "annotation": "const*"}
                 ]
             },

generator/templates/dawn_native/wgpu_structs.h

@@ -23,6 +23,8 @@ namespace dawn_native {
 {% macro render_cpp_default_value(member) -%}
     {%- if member.annotation in ["*", "const*", "const*const*"] and member.optional -%}
         {{" "}}= nullptr
+    {%- elif member.type.category == "object" and member.optional -%}
+        {{" "}}= nullptr
     {%- elif member.type.category in ["enum", "bitmask"] and member.default_value != None -%}
         {{" "}}= wgpu::{{as_cppType(member.type.name)}}::{{as_cppEnum(Name(member.default_value))}}
     {%- elif member.type.category == "native" and member.default_value != None -%}

generator/templates/webgpu_cpp.h

@@ -143,6 +143,8 @@ namespace wgpu {
 {% macro render_cpp_default_value(member) -%}
     {%- if member.annotation in ["*", "const*", "const*const*"] and member.optional -%}
         {{" "}}= nullptr
+    {%- elif member.type.category == "object" and member.optional -%}
+        {{" "}}= nullptr
     {%- elif member.type.category in ["enum", "bitmask"] and member.default_value != None -%}
         {{" "}}= {{as_cppType(member.type.name)}}::{{as_cppEnum(Name(member.default_value))}}
     {%- elif member.type.category == "native" and member.default_value != None -%}