Mojo C++ bindings: switch the existing usage of StructTraits to use the new data view interface.

mojo/public/tools/bindings/generators/cpp_templates/struct_serialization_declaration.tmpl

 {%- import "struct_macros.tmpl" as struct_macros %}
 {%- set mojom_type = struct|get_qualified_name_for_kind %}
 {%- set data_type = struct|get_qualified_name_for_kind(internal=True) %}
 
 template <>
 struct StructTraits<{{mojom_type}}, {{mojom_type}}Ptr> {
   static bool IsNull(const {{mojom_type}}Ptr& input) { return !input; }
+  static void SetToNull({{mojom_type}}Ptr* output) { output->reset(); }
 
 {%- for field in struct.fields %}
 {%-   set return_ref = field.kind|is_object_kind or
                        field.kind|is_any_handle_kind or
                        field.kind|is_interface_kind or
                        field.kind|is_associated_kind %}
 {%-   if return_ref %}
   static decltype({{mojom_type}}::{{field.name}})& {{field.name}}(
       {{mojom_type}}Ptr& input) {
     return input->{{field.name}};
   }
   static const decltype({{mojom_type}}::{{field.name}})& {{field.name}}(
       const {{mojom_type}}Ptr& input) {
     return input->{{field.name}};
   }
 {%-   else %}
   static decltype({{mojom_type}}::{{field.name}}) {{field.name}}(
       const {{mojom_type}}Ptr& input) {
     return input->{{field.name}};
   }
 {%-   endif %}
 {%- endfor %}
 
-  static bool ReadFromDataView({{mojom_type}}DataView input,
-                               {{mojom_type}}Ptr* output);
+  static bool Read({{mojom_type}}DataView input, {{mojom_type}}Ptr* output);
 };
 
 namespace internal {
 
 template <typename MaybeConstUserType>
 struct Serializer<{{mojom_type}}Ptr, MaybeConstUserType> {
   using UserType = typename std::remove_const<MaybeConstUserType>::type;
   using Traits = StructTraits<{{mojom_type}}, UserType>;
 
   static size_t PrepareToSerialize(MaybeConstUserType& input,
@@ skipping 15 matching lines @@
                                 "context", True)|indent(4)}}
       *output = result;
     } else {
       *output = nullptr;
     }
   }
 
   static bool Deserialize({{data_type}}* input,
                           UserType* output,
                           SerializationContext* context) {
-    return ReadCaller<Traits, HasReadFromDataViewMethod<Traits>::value>::Run(
-        input, output, context);
+    if (!input)
+      return CallSetToNullIfExists<Traits>(output);
+
+    {{mojom_type}}DataView data_view(input, context);
+    return Traits::Read(data_view, output);
   }
-
-
- public:
-  template <typename Traits, bool use_read_from_data_view>
-  struct ReadCaller;
-
-  template <typename Traits>
-  struct ReadCaller<Traits, false> {
-    static bool Run({{data_type}}* input,
-                    UserType* output,
-                    SerializationContext* context) {
-      {{mojom_type}}_Reader reader(input, context);
-      return Traits::Read(reader, output);
-    }
-  };
-
-  template <typename Traits>
-  struct ReadCaller<Traits, true> {
-    static bool Run({{data_type}}* input,
-                    UserType* output,
-                    SerializationContext* context) {
-      {{mojom_type}}DataView data_view(input, context);
-      return Traits::ReadFromDataView(data_view, output);
-    }
-  };
 };
 
 }  // namespace internal