Add field-initializing constructors to generated mojo structs.

mojo/public/interfaces/bindings/tests/test_structs.mojom

Index: mojo/public/interfaces/bindings/tests/test_structs.mojom
diff --git a/mojo/public/interfaces/bindings/tests/test_structs.mojom b/mojo/public/interfaces/bindings/tests/test_structs.mojom
index 683f0a56a08fe68fee7ff7b3d901978c97265495..03a0a20581bedd648ac1969a80c6a0d90f0d7f3b 100644
--- a/mojo/public/interfaces/bindings/tests/test_structs.mojom
+++ b/mojo/public/interfaces/bindings/tests/test_structs.mojom
@@ -360,6 +360,16 @@ struct MultiVersionStructV7 {
   bool f_bool;
 };
 
+// A struct where the fields are not sorted by their ordinals.
+struct ReorderedStruct {
+  [MinVersion=2]
+  int32 a@3 = 3;
+  [MinVersion=4]
+  int32 b@6 = 6;
+  [MinVersion=1]
+  int32 c@1 = 1;
+};
+
 // Used to verify that interfaces that are struct members can be defined in the
 // same file.