C bindings: Implement _Validate(), and some pre-requisites

mojom/generators/c/templates/struct.tmpl.go

Index: mojom/generators/c/templates/struct.tmpl.go
diff --git a/mojom/generators/c/templates/struct.tmpl.go b/mojom/generators/c/templates/struct.tmpl.go
index 9bdc77819386e067f654ddcb5c7ab70c2506160b..7cefe7824c66dc78fe74c3fbfdc295b1e72ab203 100644
--- a/mojom/generators/c/templates/struct.tmpl.go
+++ b/mojom/generators/c/templates/struct.tmpl.go
@@ -51,6 +51,10 @@ void {{$struct.Name}}_DecodePointersAndHandles(
   struct {{$struct.Name}}* inout_struct, uint32_t in_struct_size,
   MojoHandle inout_handles[], uint32_t in_num_handles);
 
+MojomValidationResult {{$struct.Name}}_Validate(
+  const struct {{$struct.Name}}* in_struct, uint32_t in_struct_size,
+  uint32_t in_num_handles);
+
 {{end}}
 `
 
@@ -89,5 +93,18 @@ void {{$struct.Name}}_DecodePointersAndHandles(
     inout_handles, in_num_handles);
 }
 
+MojomValidationResult {{$struct.Name}}_Validate(
+  const struct {{$struct.Name}}* in_struct, uint32_t in_struct_size,
+  uint32_t in_num_handles) {
+  struct MojomValidationContext context = {
+    .next_handle_index = 0,
+    .next_pointer = (char*)in_struct + in_struct->header_.num_bytes,
+  };
+  return MojomStruct_Validate(
+    &{{$struct.Name}}__TypeDesc,
+    (struct MojomStructHeader*)in_struct, in_struct_size, in_num_handles,
+    &context);
+}
+
 {{end}}
 `