Implement unions as members of structs.

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

Index: mojo/public/tools/bindings/generators/mojom_cpp_generator.py
diff --git a/mojo/public/tools/bindings/generators/mojom_cpp_generator.py b/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
index 8b7e2197c08b35824826ac7498b79cd43c82ac03..d037b2efaeb1c4e3928b4edfe26e859010a532b2 100644
--- a/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
+++ b/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
@@ -147,7 +147,7 @@ def GetCppResultWrapperType(kind):
 def GetCppWrapperType(kind):
   if mojom.IsEnumKind(kind):
     return GetNameForKind(kind)
-  if mojom.IsStructKind(kind):
+  if mojom.IsStructKind(kind) or mojom.IsUnionKind(kind):
     return "%sPtr" % GetNameForKind(kind)
   if mojom.IsArrayKind(kind):
     return "mojo::Array<%s>" % GetCppArrayArgWrapperType(kind.kind)
@@ -206,6 +206,8 @@ def GetCppFieldType(kind):
   if mojom.IsStructKind(kind):
     return ("mojo::internal::StructPointer<%s_Data>" %
         GetNameForKind(kind, internal=True))
+  if mojom.IsUnionKind(kind):
+    return "%s_Data" % GetNameForKind(kind, internal=True)
   if mojom.IsArrayKind(kind):
     return "mojo::internal::ArrayPointer<%s>" % GetCppType(kind.kind)
   if mojom.IsMapKind(kind):